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2017  Nov 1 - Dec 21

2018  Feb 7 - Apr 3
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2018  Apr 11 - Jun 4
2018  Proposal/BTR deadline: 2/1/18

Talk Abstracts


"Pressure-directed Assembly of New Classes of Nanocrystal Superlattices and Nanostructures"

Hongyou Fan
Sandia National Laboratories, Albuquerque, NM
NSF/University of New Mexico, Center for Micro-Engineered Materials, Dept. of Chemical and Nuclear Engineering, Albuquerque, NM

Abstract: Naturally occurred folding and unfolding systems such as self-assembled DNA bundles prove natural designs are hierarchical, with structures and property on multiple scales through interactions of subunits or building blocks. Mimicking these designs in fabrication of active materials requires a clear picture of energy landscaping that govern local interactions such as hydrogen bonding, van der Waals interactions, dipole-dipole interaction, capillary forces, etc, which will provide correct thermodynamic end points as well as facile kinetics for precise control of hierarchical structure for target function. To date, fabrications of active nanostructures have been conducted at ambient pressure and largely relied on these specific chemical or physical interactions. Here we show using Pressure-Directed Assembly (PDA) method we recently demonstrated, as an artificial tool, we can emulate natural folding and unfolding processes to explore energy landscaping that govern local interactions, to design new classes of active materials with structure and function that are not attainable for current materials, and to investigate new property resulted from the folding and unfolding processes. We show that under a hydrostatic pressure field, the unit cell dimension of a 3D ordered nanoparticle arrays can be manipulated to reversibly shrink and swell during compression and release of pressure, allowing precise tuning of interparticle symmetry and spacing, ideal for controlled investigation of distance-dependent energy couplings and collective chemical and physical property such as surface plasmon resonance. Moreover, beyond a threshold pressure, nanoparticles are forced to contact and sinter, forming new classes of chemically and mechanically stable 1-3D nanostructures that cannot be manufactured by current top-down or bottom-up methods. Depending on the orientation of the initial nanoparticle arrays, 1-3D ordered nanostructures (Au, Ag, CdSe, C60, etc) including nanorod, nanowire, nanosheet, and nanoporous network can be fabricated. Guided by computational simulations, we are able to rationalize the PDA of nanoparticle arrays for predictable nanostructures. PDA method mimics embossing and imprinting manufacturing processes and opens exciting new avenues for study folding and unfolding of active materials during compression (folding) and pressure release (unfolding). Exerting pressure-dependent control over the structure of nanoparticle or building block arrays provides a unique and robust system to understand collective chemical and physical characteristics of nanocrystal superlattices.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.


"Self-assembled Superstructure of Octahedral and Cubic Nanocrystals"

Jun Zhang1, Zhiping Luo2, Zewei Quan1, Welley Loc1, Yuxuan Wang1, Zhongwu Wang3, Detlef-M. Smilgies3 and Jiye Fang1
1Dept. of Chemistry and MSE Program, State University of New York at Binghamton, Binghamton, NY
2Microscopy and Imaging Center, Texas A&M University, College Station, TX
3Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY

Abstract: A structural study on self-assembled superlattices of Pt3Ni nano-octahedra and PbS nanocubes is presented. The shape-controlled building blocks were synthesized through a wet-chemical approach and their morphologies were well characterized. Structure-defined superlattices of these high-quality nanocrystals were subsequently prepared, respectively. The superlattices were investigated using several techniques including transmission electron microscopic tomography, grazing-incidence small-angle X-ray scattering method as well as synchrotron X-ray diffraction. The packing structure in each superlattice system was determined and is discussed.


"Nanocrystal Superlattices: a model system for artificial solids"

Tobias Hanrath1, Kaifu Bian1, Josh J. Choi1, Zhongwu Wang2, Detlef-M. Smilgies2
1Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY
2Cornell High Synchrotron Source, Cornell University, Ithaca, NY

Abstract:  A Compared to the immense progress made in synthetic control of size, shape and composition of individual colloidal nanocrystals, the structural control over their ordered assemblies is less well developed, but rapidly evolving. We summarize recent experiments at CHESS that provided new fundamental insights into the directed self-assembly of nanocrystal superlattices allotropes. Specifically, we found that identical nanocrystal building blocks can be assembled into oriented superstructures with predefined symmetries, including face-centered cubic (fcc), body-centered cubic (bcc), and a variety of body-centered tetragonal (bct) structures. Simultaneous small- and wide-angle X-ray scattering data from D-1 illustrate the coaxial alignment of the nearly spherical lead salt nanocrystals on their superlattice sites. Importantly, our in situ experiments show that the coherent nanocrystal superlattice symmetry distortion is driven by the orientational ordering of the constituent nanocrystals; this process is analogous to martensitic phase transitions in atomic crystals. The ability to direct the self-assembly into superlattices with predefined symmetries provides a fertile opportunity space for experiments elucidating fundamental structure-property relationships.

More recently, we investigated the structural stability of colloidal PbS nanocrystals superlattice allotropes with fcc or bcc symmetry under pressure within the diamond anvil cell at B2. Small angle-X-ray scattering SAXS analysis showed that the nanocrystal packing density is higher in the bcc than in the fcc SL, which we attribute to the cuboctahedra shape of the constituent nanocrystals. Using the high-pressure rock salt/orthorhombic phase transition as a stability indicator, we discovered that the transition pressure for nanocrystals in a bcc superlattice occurs at 8.5 GPa; which is 1.5 GPa higher than the transition pressure (7.0 GPa) observed for a fcc superlattice. The higher structural stability in the bcc superlattice is attributed primarily to the effective absorption of loading force in specific SL symmetry and to a lesser extent to the surface energy of the nanocrystals. The experimental results provide new insights into the fundamental relationship between the symmetry of the self-assembled SL and the structural stability of the constituent NCs.


"Prediction of Nanocrystal Morphology and Assembly"

Richard Hennig
Materials Science and Engineering, Cornell University, Ithaca, NY

Abstract:  Predictions of structure formation by computational methods have the potential to accelerate materials discovery and design. The self-assembly of nanocrystals into mesoscale superlattices provides a path to the design of materials with tunable electronic, physical and chemical properties for various applications. The self-assembly is controlled by the nanocrystal shape and ligand-mediated interactions between them. To understand this, it is necessary to know the effect of the ligands on the surface energies (which tune the nanocrystal shape), as well as the relative coverage of the different facets (which control the interactions). We will discuss how ab-initio calculations of surface and ligand-binding energies for PbSe nanocrystals predicts the equilibrium shape of the nanocrystals and a transition from octahedral to cubic when increasing the ligand concentration during synthesis[1]. Our results furthermore suggest that the experimentally observed transformation of the nanocrystal superlattice structure from fcc to bcc is caused by the preferential detachment of ligands from particular facets, leading to anisotropic ligand coverage[2].


[1] C.R. Bealing, W.J. Baumgardner, J.J. Choi, T. Hanrath, and R. G Hennig; ACS Nano (2012)
[2] J.J. Choi, C.R. Bealing, K. Bian, K.J. Hughes, W. Zhang, D.-M. Smilgies, R.G. Hennig, James R. Engstrom, and Tobias Hanrath; J. Am. Chem. Soc. 133, 3131 (2011)


"Solution Bio-SAXS in High-throughput at SIBYLS"

Greg Hura
Physical Biosciences Division at Lawrence Berkeley National Lab, CA

Abstract:  Greg Hura Physical Biosciences Division at Lawrence Berkeley National Lab, CA Structural analysis by small angle X-ray scattering of biological macromolecules efficiently enables the characterization of shape and assembly for nearly any purified target. Crystallography has provided a deep and broad survey of macromolecular structure. Shape and assembly from SAXS in combination with available structures is often enough to answer critical mechanistic questions both enhancing the value of a structure and identifying other high impact crystallographic projects. Here we’ll present our high throughput SAXS data collection and analysis pipeline as applied to DNA repair targets and metabolic pathways. We’ll introduce ways in which high-throughput SAXS enhances capabilities for the fabrication of nanomaterials. In particular we’ve been developing gold nanocrystal labels for DNA as a monitor of DNA repair processes. Given the number of gene products involved in metabolic networks, SAXS will play an important role in characterizing the structure of each individually, in complex with partners, and in various contexts. SAXS is well positioned to efficiently bridge the rapid output of bioinformatics and the relatively slow output of high resolution structural techniques.


"Water and Protein Dynamical Transition"

Chae Un Kim1, Mark W. Tate2 and Sol M. Gruner1,2
1Cornell High Energy Synchrotron Source (CHESS) and Macromolecular Crystallography at CHESS (MacCHESS), Cornell University, Ithaca, NY
2Physics Department, Cornell University, Ithaca NY

Abstract:  Proteins must fluctuate to perform cellular functions, such as enzymatic catalysis, protein-protein interactions, and interactions with DNA and RNA. When proteins are cooled the conformational fluctuations dampen and eventually stop, typically at 200-240 K. This is called a protein dynamical transition. Proteins below the transition temperature show no appreciable biological function. Above the transition temperature flexibility is restored and the protein becomes increasingly biologically active. The underlying physical origin of the protein dynamical transition is controversial. Water is thought to be involved, since proteins below the transition temperature behave as if they are dehydrated. But the exact nature of the water-protein coupling is not clearly understood. We studied protein dynamics inside high-pressure cryocooled protein crystals and observed a protein dynamical transition as low as 110K[1]. This unexpected protein dynamical transition precisely correlated with the cryogenic phase transition of water from high-density amorphous to low-density amorphous state[2]. The results provide new insights into the underlying mechanism of protein dynamical transition and its relationship with the unusual physical properties of supercooled water.


[1] Chae Un Kim, Mark W. Tate and Sol M. Gruner; "Protein Dynamical Transition at 110 K", Proc. Natl. Acad. Sci. 108, 20897-20901 (2011)
[2] Chae Un Kim, Buz Barstow, Mark W. Tate and Sol M. Gruner; "Evidence for Liquid Water During the High-density to Low-density Amorphous Ice Transition", Proc. Natl. Acad. Sci. 106, 4596-4600 (2009)


"Nanocrystal Superlattices: a model system for artificial solids"

Brian W. Goodfellow1, Michael R. Rasch1, Detlef-M. Smilgies2, Brian A. Korgel1
1Dept. of Chemical Engineering, Texas Materials Institute, Center for Nano- and Molecular Science and Technology, The University of Texas at Austin, Austin, TX
2Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY

Abstract:  Dense collections of hard sphere particles order into close-packed face-centered cubic (fcc) lattices to maximize free volume entropy. Sterically-stabilized nanocrystals have relatively short-range repulsive interaction potentials and also tend to order into fcc superlattices. However, nanocrystal superlattices with non-close-packed body-centered cubic (bcc) structure are also relatively common. As examples, we have observed bcc superlattices of 1.8 nm dodecanethiol-capped Au nanocrystals, 3.7 nm oleic acid-capped PbS nanocrystals, and 7.9 nm oleic acid-capped PbSe nanocrystals. We argue that bcc superlattices can be favored over fcc when entropic ligand packing frustration overcomes the packing entropy of the spheres. This idea is consistent with our observation of a superlattice thickness-dependent change in structure from hexagonally close-packed monolayers to bcc superlattices in nanocrystal films. We also find that {112} twin planes are common to bcc superlattices.

The organic capping ligands are also central to nanocrystal superlattice phase behavior and structural changes with heating. Small angle X-ray scattering (SAXS) revealed that superlattices of organic ligand-stabilized gold (Au) nanocrystals can undergo a complex series of structural phase transitions at elevated temperature. For example, dodecanethiol-capped Au nanocrystal superlattices can undergo transitions from body-centered cubic (bcc) to hexagonal close-packed (hcp) structure, followed by the formation of simple cubic (sc) AB13 and hexagonal (hex) AB5 binary superlattices before decomposing at high temperature to bicontinuous domains of Au and hydrocarbon. Transmission electron microscopy (TEM) revealed that these transformations result from Au nanocrystal growth during heating, which combined with partial desorption of the ligand shell, forces the observed changes in superlattice symmetry. These observations again suggest that ligand packing entropy plays an important role in determining superlattice structure.


"Computational Prediction of Flexible Regions in Proteins that Interact with Ligands"

Markus Lill
Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, IN

Abstract: Molecular recognition between receptors and ligands through non-covalent association plays a fundamental role in virtually all biochemical processes in living organisms. Several computational concepts have been devised to study protein-ligand binding. These techniques are routinely used in academia and industry for identifying and optimizing potential drug candidates. While those methods have been widely used to attain a qualitative understanding of ligand binding to proteins, a current challenge is to quantify their interaction in a reasonable amount of time. One major issue is that the protein in reality can adapt its shape and properties upon each individual ligand binding to it (induced protein fit). In this context, I will present our development of new concepts (Software: Limoc and CorLps) incorporating protein flexibility into protein-ligand docking.

Flexible loop regions play a critical role in the biological function of many proteins and have been shown to be involved in ligand binding. In the context of structure-based drug design, using or predicting an incorrect loop configuration can be detrimental to the study if the loop is capable of interacting with the ligand. Furthermore, loop regions are often spatially in close proximity to one another and their mutual interactions stabilize their conformations. Our new concept, titled CorLps, is capable of simultaneously predicting such interacting loop regions. After introducing the novel method, I will demonstrate that predicting interacting loops with CorLps is superior to sequential prediction of the two interacting loop regions. In a subsequent study, we tested CorLps for predicting loop regions that are potentially stabilized by interacting ligands. Whereas native-like loop conformations can be generated with CorLps, our analysis with different scoring metrics demonstrated that optimal ranking of native-like loop configurations is still a difficult challenge and the choice of the "best" scoring function appears to be system dependent.

I also will highlight our new methodology, titled Limoc, which generates an ensemble of holo-like protein structures relevant for binding of structurally diverse ligands starting from a single apo or holo X-ray structure.


"Flexibility Drives Substrate Promiscuity in Cyclooxygenase-2"

Michael G. Malkowski
Hauptman-Woodward Medical Research Institute and Department of Structural Biology, State University of New York at Buffalo, Buffalo NY

Abstract:  The cyclooxygenases (COX-1 and COX-2) generate prostaglandin H2 from arachidonic acid (AA). In its catalytically productive conformation, AA binds within the cyclooxygenase channel with its carboxylate near Arg-120 and Tyr-355 and w-end located within a hydrophobic groove above Ser-530. While AA is the preferred substrate for both isoforms, COX-2 can oxygenate a broad spectrum of substrates. Mutational analyses have established that an interaction of the carboxylate of AA with Arg-120 is required for high-affinity binding by COX-1, but not COX-2, suggesting that hydrophobic interactions between the w-end of substrates and cyclooxygenase channel residues play a significant role in COX-2-mediated oxygenation. We used structure-function analyses to investigate the role that Arg-120 and residues lining the hydrophobic groove play in the binding and oxygenation of substrates by murine (mu) COX-2. Mutations to individual amino acids within the hydrophobic groove exhibited decreased rates of oxygenation towards AA, with little effect on binding. R120A muCOX-2 oxygenated 18-carbon ω-6 and ω-3 substrates, albeit at reduced rates, indicating that an interaction with Arg-120 is not required for catalysis. Structural determinations of Co3+-protoporphyrin IX reconstituted muCOX-2 with α-linolenic acid and G533V muCOX-2 with AA indicate that proper bis-allylic carbon alignment is the major determinant for efficient substrate oxygenation by COX-2. Overall, these findings implicate Arg-120 and hydrophobic groove residues as determinants that govern proper alignment of the bis-allylic carbon below Tyr-385 for catalysis in COX-2 and confirms nuances between COX isoforms that explain substrate promiscuity.

This work was supported by NIH NIGMS grant R01 GM077176 and by an Arthritis Investigator Award from the Arthritis Foundation as part of the Segal Osteoarthritis Initiative.


"Structural Basis of RNA Recognition and Activation by Innate Immune Receptor RIG-I"

Joseph Marcotrigiano
Center for the Advanced Biotechnology and Medicine, Rutgers University, Piscataway, NJ

Abstract:  RIG-I (Retinoic acid Inducible Gene - I) is a cytoplasmic pathogen recognition receptor that differentiates between viral and cellular RNAs. Upon binding to such PAMP motifs, RIG-I initiates a signaling cascade that induces innate immune defenses and inflammatory cytokines to establish an antiviral state. The RIG-I pathway is highly regulated and aberrant signaling leads to apoptosis, altered cell differentiation, inflammation, autoimmune diseases and cancer. RIG-I is activated by blunt-ended double-stranded (ds)RNA with or without a 5′-triphosphate (ppp), single-stranded RNA marked by a 5′-ppp and polyuridine sequences. The RIG-I helicase and repressor domains (RD) are responsible for RNA binding as foreign and activate the two CAspase Recruitment Domains (CARD) on the amino terminus for signaling. To understand the synergy between helicase and RD for RNA binding and how ATP hydrolysis contributes to RIG-I activation, we determined the structure of human RIG-I helicase-RD in complex with dsRNA and an ATP-analog. Helicase-RD organizes into a ring with the helicase utilizing previously uncharacterized motifs to specifically recognize dsRNA. In addition, small angle X-ray scattering (SAXS), limited proteolysis, and differential scanning fluorimetry suggest that RIG-I is in an extended and flexible conformation that compacts upon binding RNA. These results provide a greater mechanistic understanding of the cellular response and immune activation to viral infection.


"Chemical Transformations in Nanoparticles, Studied through X-ray Absorption Spectroscopy"

Richard Robinson
Dept. of Materials Science, Cornell University, Ithaca, NY

Abstract: Nanoscale systems can display interesting and unique transformation kinetics that increase the structural complexity of the original material. Some of the most interesting nanoparticle morphologies and heterostructures in recent years have come from chemical transformations applied to nanoparticles, for example Kirkendall hollowing and partial cation exchange. Characterization of the transformation routes to form complex final structures is one of the major challenges in nanoscience. A more complete understanding of the transformation pathways would provide directions to improve synthesis techniques, leading to optimization of nanoparticles for use in applications. It also would provide insight into the control of nanoparticle chemical and physical properties. X-ray absorption spectroscopy (XAS) is a useful and innovative technique to study nanoscale systems where other characterization techniques fail due to resolution and sensitivity limits. Techniques such as x-ray diffraction (XRD), for example, are insufficient to analyze some nanoparticle systems that lack long-range order, particularly in intermediate phases. In XAS the XANES region provides details about sample geometric and electronic structure, and the EXAFS region provides short-range order, on the subnanometer scale, making it particularly important for nanoscale and amorphous materials. Through the combination of these techniques, along with TEM and DFT calculations, a thorough characterization and analysis of chemical transformations in nanoparticles is provided in this talk.

In this talk I will discuss our recent work studying chemical transformations of nanoparticles through x-ray absorption spectroscopy (XAS). I will discuss our work on the structural evolution and the diffusion processes which occur during the phase transformation of nanoparticle ε-Co to Co2P to CoP, from a reaction with tri-n-octylphosphine (TOP). Extended X-ray absorption fine structure (EXAFS) investigations were used to elucidate the changes in the local structure of cobalt atoms which occur as the chemical transformation progresses. Results from EXAFS, transmission electron microscopy, X-ray diffraction, and density functional theory calculations reveal that the inward diffusion of phosphorus is more favorable at the beginning of the transformation from ε-Co to Co2P by forming an amorphous Co-P shell, while retaining a crystalline cobalt core. When the major phase of the sample turns to Co2P, the diffusion processes reverse and cobalt atom out-diffusion is favored, leaving a hollow void, characteristic of the nanoscale Kirkendall effect.

I will also discuss our work using XAS to examine nickel and nickel phosphide nanoparticles, examining differences between the phases. EXAFS reveals that there is a significant amount of phosphorus in nickel samples, which appear as fcc nickel in XRD. This suggests that Ni-P intermediate phases retain the long range order of a phosphorus-poor structure despite excess Ni-P bonds with short-range ordering. We compare the long-range structural characterization by XRD to the short-range order displayed by EXAFS in order to investigate the limitations of XRD in nanoparticle characterization. This enables us to resolve the nanoparticle phase transition properties and diffusion mechanisms, which can lead to optimization of nanoparticle synthesis as well as nanoparticle use in device technology.


"A Combinatorial Technique for the Calorimetric Analysis of Nanoscale Quantities of Materials"

Joost J. Vlassak1, John M. Gregoire1, Patrick J. McCluskey1, Darren Dale2, Shiyan Ding3, and Jan Schroers3
1School of Engineering and Applied Sciences, Harvard University, Cambridge, MA
2Cornell High Synchrotron Source, Cornell University, Ithaca, NY
3Mechanical Engineering, Yale University, New Haven, CT

Abstract:  Calorimetric studies of bulk metallic glasses are typically performed at heating or cooling rates smaller than about 102 K/s, because of experimental limitations associated with bulk calorimeters. While faster cooling rates can be attained in uncontrolled quench procedures, the systematic study of glass formation and crystallization kinetics is limited by these experimental capabilities. By employing the thin-film architecture of the parallel nano-scanning calorimeter (PnSC)[1], we perform calorimetric characterization of glass formation, crystallization, and melting with 102 – 104 K/s heating and cooling rates (Fig). These experiments are performed over an array of 22 compositions in the glass-forming system Au-Si-Cu[2]. In-situ synchrotron X-ray diffraction (XRD) experiments provide characterization of the crystalline and amorphous components of as a function of quench rate and composition. Combining these XRD results with the PnSC scans enables to decode in an effective manner the complex crystallization of these alloys. More generally, the power of combining these experimental techniques will be discussed not only in the context of the characterization of phase transformations in materials[3], but also with regard to the high-throughput probing of glass physics.

Five sets of experiments for a single sample (Autyle3">30Si21, 52 nmol) ordered by quench rate. Each row contains the quench rate (a), the resulting phase composition (b) and the calorimetry trace upon subsequent heating (c).


[1] P.J. McCluskey, J.J. Vlassak; J. of Mater. Res. 25, 2086 (2010)
[2] J.M. Gregoire, P.J. McCluskey, D. Dale, S. Ding, J. Schroers, J.J. Vlassak; Scripta Mater. 66, 178(2011)
[3] Y. Motemani, P. J. McCluskey, C. Zhao, M. J. Tan, J. J. Vlassak, Acta Mater. 59 (2012)


"Conformational Flexibility in the Allosteric Regulation of Human UDP-α-D-glucose 6-dehydrogenase"

Nicholas C. Sennett, Renuka Kadirvelraj, Greg Custer and Zachary A. Wood
Dept. of Biochemistry and Molecular Biology, University of Georgia, Athens GA

Abstract: UDP-α-D-xylose (UDX) acts as a feedback inhibitor to human UDP-α-D-glucose-6-dehydrogenase (hUGDH) by activating an unusual allosteric switch, the Thr131-loop. UDX binding induces the Thr131-loop to translate ~5Å through the protein core, changing packing interactions and rotating a helix (α6136-144) to favor the formation of an inactive hexameric complex. But how does this conformational change occur given the steric packing constraints of the protein core? To answer this question, we deleted Val132 from the Thr131-loop to mimic an intermediate state in the allosteric transition. The 2.3Å resolution crystal structure of the deletion construct (∆132) reveals a ‘hinge-bending’ motion that exposes the Thr131-loop to solvent. This open conformation relaxes the steric constraints to facilitate the repacking of the core. Sedimentation velocity studies show that the open conformation stabilizes the ∆132 construct as a hexamer with point group symmetry 32, similar to the wild-type enzyme. In contrast, the UDX-inhibited enzyme forms a lower symmetry, U-shaped hexameric complex. We show that the ∆132 and UDX-inhibited structures have similar hexamer-building interfaces, suggesting that the hinge-bending motion represents a path for the allosteric transition between the different hexameric states. Based on (i) main-chain flexibility and (ii) a model of the conformational change, we propose that the hinge-bending can occur as a concerted motion between adjacent subunits in the high symmetry hexamer. We combine these results in a structurally detailed model for allosteric feedback inhibition and substrate-product exchange during the catalytic cycle.


"Use of CHESS Beamlines for X-ray Crystallography and Small Angle X-ray Scattering Projects from Pennsylvania State University"

Neela Yennawar
Penn State University, PA

Abstract:  Two recent projects from Pennsylvania State University that used CHESS facility will be presented. The first one is the crystal structure determination of a unique protein from the genome of Methanosarcina acetivorans, a methane-producing organism from Archaea. The novel chimeric protein contains a plant-type ferredoxin/thioredoxin reductase-like catalytic domain in the N-terminal region with a 4Fe-4S cluster and a bacterial-like rubredoxin domain with a one Fe center in the C-terminal region. The two iron centers are in close proximity and may be involved in an unusual electron transfer pathway leading to disulfide reduction in its substrates. The second project that will be presented is the small angle X-ray scattering and X-ray crystal structure of sheep-liver sorbitol dehydrogenase. The crystal structure details the interactions of a biologically active tetramer. The substrate-binding pocket is close to the tetramer interface. Small-angle X-ray scattering verifies the disposition of the active tetramer in solution.