The closest packing of spheres : a unifying basis for crystal structures /

"AES research and development report"--Cover.

Train wreck Crystal Falls, Mich.

verso: this is a wreack [sic] we had some time ago, were [sic] you see the cross, the engineer was pined [sic[ two feet in the ground you can imagine what he looked lik [sic]

Crystal structures of fusion proteins with large-affinity tags

The fusion of a protein of interest to a large-affinity tag, such as the maltose-binding protein (MBP), thioredoxin (TRX), or glutathione-S-transferase (GST), can be advantageous in terms of increased expression, enhanced solubility, protection from proteolysis, improved folding, and protein purification via affinity chromatography. Unfortunately, crystal growth is hindered by the conformational heterogeneity induced by the fusion tag, requiring that the tag is removed by a potentially problematic cleavage step. The first three crystal structures of fusion proteins with large-affinity tags have been reported recently. All three structures used a novel strategy to rigidly fuse the protein of interest to MBP via a short three- to five-amino acid spacer. This strategy has the potential to aid structure determination of proteins that present particular experimental challenges and are not conducive to more conventional crystallization strategies (e.g., membrane proteins). Structural genomics initiatives may also benefit from this approach as a way to crystallize problematic proteins of significant interest.

The 2.2 A crystal structure of a pocilloporin pigment reveals a nonplanar chromophore conformation

Reef-building corals contain host pigments, termed pocilloporins, that function to regulate the light environment of their resident microalgae by acting as a photoprotectant in excessive sunlight. We have determined the crystal structure of an intensely blue, non-fluorescent pocilloporin to 2.2 Angstrom resolution and a genetically engineered fluorescent variant to 2.4 Angstrom resolution. The pocilloporin chromophore structure adopts a markedly different conformation in comparison with the DsRed chromophore, despite the chromophore sequences (Gin-Tyr-Gly) being identical; the tyrosine ring of the pocilloporin chromophore is noncoplanar and in the trans configuration. Furthermore, the fluorescent variant adopted a noncoplanar chromophore conformation. The data presented here demonstrates that the conformation of the chromophore is highly dependent on its immediate environment.

The R8-BC8 phases and crystal growth in monocrystalline silicon under microindentation with a spherical indenter

The morphology and distribution of high-pressure metastable phases BC8 and R8, formed in monocrystalline silicon under microindentation, were identified and assessed using transmission electron microscopy nanodiffraction analysis. It was discovered that the crystal growth inside the transformation zone was stress-dependent with large crystals in its central region. The crystal size could also be increased using higher maximum indentation loads. The BC8 and R8 phases distributed unevenly across the transformation zone, with BC8 crystals mainly in the center of the zone and smaller R8 fragments in the peripheral regions. Such phase distribution was in agreement with the theoretical residual stress analysis.

Ultrastructure, aggregation-state, and crystal growth of biogenic nanocrystalline sphalerite and wurtzite

In this study, we investigated the size, submicrometer-scale structure, and aggregation state of ZnS formed by sulfate-reducing bacteria (SRB) in a SRB-dominated biofilm growing on degraded wood in cold (Tsimilar to8degreesC), circumneutral-pH (7.2-8.5) waters draining from an abandoned, carbonate-hosted Pb-Zn mine. High-resolution transmission electron microscope (HRTEM) data reveal that the earliest biologically induced precipitates are crystalline ZnS nanoparticles 1-5 nm in diameter. Although most nanocrystals have the sphalerite structure, nanocrystals of wurtzite are also present, consistent with a predicted size dependence for ZnS phase stability. Nearly all the nanocrystals are concentrated into 1-5 mum diameter spheroidal aggregates that display concentric banding patterns indicative of episodic precipitation and flocculation. Abundant disordered stacking sequences and faceted, porous crystal-aggregate morphologies are consistent with aggregation-driven growth of ZnS nanocrystals prior to and/or during spheroid formation. Spheroids are typically coated by organic polymers or associated with microbial cellular surfaces, and are concentrated roughly into layers within the biofilm. Size, shape, structure, degree of crystallinity, and polymer associations will all impact ZnS solubility, aggregation and coarsening behavior, transport in groundwater, and potential for deposition by sedimentation. Results presented here reveal nanometer- to micrometer-scale attributes of biologically induced ZnS formation likely to be relevant to sequestration via bacterial sulfate reduction (BSR) of other potential contaminant metal(loid)s, such as Pb2+, Cd2+, As3+ and Hg2+, into metal sulfides. The results highlight the importance of basic mineralogical information for accurate prediction and monitoring of long-term contaminant metal mobility and bioavailability in natural and constructed bioremediation systems. Our observations also provoke interesting questions regarding the role of size-dependent phase stability in biomineralization and provide new insights into the origin of submicrometer- to millimeter-scale petrographic features observed in low-temperature sedimentary sulfide ore deposits.

Partial regularity of weak solutions of the liquid crystal equilibrium system

For a parameter, we consider the modified relaxed energy of the liquid crystal system. Each minimizer of the modified relaxed energy is a weak solution to the liquid crystal equilibrium system. We prove the partial regularity of minimizers of the modified relaxed energy. We also prove the existence of infinitely many weak solutions for the special boundary value x.

The crystal structures of Klebsiella pneumoniae acetolactate synthase with enzyme-bound cofactor and with an unusual intermediate

Acetohydroxyacid synthase (AHAS) and acetolactate synthase (ALS) are thiamine diphosphate (ThDP)-dependent enzymes that catalyze the decarboxylation of pyruvate to give a cofactor-bound hydroxyethyl group, which is transferred to a second molecule of pyruvate to give 2-acetolactate. AHAS is found in plants, fungi, and bacteria, is involved in the biosynthesis of the branched-chain amino acids, and contains non-catalytic FAD. ALS is found only in some bacteria, is a catabolic enzyme required for the butanediol fermentation, and does not contain FAD. Here we report the 2.3-Angstrom crystal structure of Klebsiella pneumoniae ALS. The overall structure is similar to AHAS except for a groove that accommodates FAD in AHAS, which is filled with amino acid side chains in ALS. The ThDP cofactor has an unusual conformation that is unprecedented among the 26 known three-dimensional structures of nine ThDP-dependent enzymes, including AHAS. This conformation suggests a novel mechanism for ALS. A second structure, at 2.0 Angstrom, is described in which the enzyme is trapped halfway through the catalytic cycle so that it contains the hydroxyethyl intermediate bound to ThDP. The cofactor has a tricyclic structure that has not been observed previously in any ThDP-dependent enzyme, although similar structures are well known for free thiamine. This structure is consistent with our proposed mechanism and probably results from an intramolecular proton transfer within a tricyclic carbanion that is the true reaction intermediate. Modeling of the second molecule of pyruvate into the active site of the enzyme with the bound intermediate is consistent with the stereochemistry and specificity of ALS.