A molecular MoS₂ edge site mimic for catalytic hydrogen generation

Inorganic solids are an important class of catalysts that often derive their activity from sparse active sites that are structurally distinct from the inactive bulk. Rationally optimizing activity is therefore beholden to the challenges in studying these active sites in molecular detail. Here, we report a molecule that mimics the structure of the proposed triangular active edge site fragments of molybdenum disulfide (MoS(2)), a widely used industrial catalyst that has shown promise as a low-cost alternative to platinum for electrocatalytic hydrogen production. By leveraging the robust coordination environment of a pentapyridyl ligand, we synthesized and structurally characterized a well-defined Mo(IV)-disulfide complex that, upon electrochemical reduction, can catalytically generate hydrogen from acidic organic media as well as from acidic water.     

Hybrid ribosome formation from Escherichia coli and chloroplast ribosome subunits

A 70S ribosome was prepared from a 30S ribosome subunit from Euglena gracilis chloroplasts and a 50S ribosome subunit from Escherichia coli. This hybrid ribosome was active in polyuridylic acid-directed polyphenylalanine synthesis.     

A Ni-Fe-Cu center in a bifunctional carbon monoxide dehydrogenase/acetyl-CoA synthase

A metallocofactor containing iron, sulfur, copper, and nickel has been discovered in the enzyme carbon monoxide dehydrogenase/acetyl-CoA (coenzyme A) synthase from Moorella thermoacetica (f. Clostridium thermoaceticum). Our structure at 2.2 angstrom resolution reveals that the cofactor responsible for the assembly of acetyl-CoA contains a [Fe4S4] cubane bridged to a copper-nickel binuclear site. The presence of these three metals together in one cluster was unanticipated and suggests a newly discovered role for copper in biology. The different active sites of this bifunctional enzyme complex are connected via a channel, 138 angstroms long, that provides a conduit for carbon monoxide generated at the C-cluster on one subunit to be incorporated into acetyl-CoA at the A-cluster on the other subunit.     

The MerR metalloregulatory protein binds mercuric ion as a tricoordinate, metal-bridged dimer

Bacterial MerR proteins are dimeric DNA-binding proteins that mediate the Hg(II)-dependent induction of mercury resistance operons. Site-directed mutagenesis of the Bacillus sp. RC607 MerR protein reveals that three of four Cys residues per monomer are required for Hg(II) binding at the single high-affinity binding site. Inactive mutant homodimers can exchange subunits to form heterodimers active for Hg(II) binding. Studies of a heterodimer retaining only three of eight cysteine residues per dimer reveal that Cys79 in one subunit and Cys114 and Cys123 in the second subunit are necessary and sufficient for high-affinity Hg(II) binding in an asymmetric, subunit bridging coordination complex.     

Direct observation of molecular preorganization for chirality transfer on a catalyst surface

The chemisorption of specific optically active compounds on metal surfaces can create catalytically active chirality transfer sites. However, the mechanism through which these sites bias the stereoselectivity of reactions (typically hydrogenations) is generally assumed to be so complex that continued progress in the area is uncertain. We show that the investigation of heterogeneous asymmetric induction with single-site resolution sufficient to distinguish stereochemical conformations at the submolecular level is finally accessible. A combination of scanning tunneling microscopy and density functional theory calculations reveals the stereodirecting forces governing preorganization into precise chiral modifier-substrate bimolecular surface complexes. The study shows that the chiral modifier induces prochiral switching on the surface and that different prochiral ratios prevail at different submolecular binding sites on the modifier at the reaction temperature.     

Crystal structure of the eukaryotic 60S ribosomal subunit in complex with initiation factor 6

Protein synthesis in all organisms is catalyzed by ribosomes. In comparison to their prokaryotic counterparts, eukaryotic ribosomes are considerably larger and are subject to more complex regulation. The large ribosomal subunit (60S) catalyzes peptide bond formation and contains the nascent polypeptide exit tunnel. We present the structure of the 60S ribosomal subunit from Tetrahymena thermophila in complex with eukaryotic initiation factor 6 (eIF6), cocrystallized with the antibiotic cycloheximide (a eukaryotic-specific inhibitor of protein synthesis), at a resolution of 3.5 angstroms. The structure illustrates the complex functional architecture of the eukaryotic 60S subunit, which comprises an intricate network of interactions between eukaryotic-specific ribosomal protein features and RNA expansion segments. It reveals the roles of eukaryotic ribosomal protein elements in the stabilization of the active site and the extent of eukaryotic-specific differences in other functional regions of the subunit. Furthermore, it elucidates the molecular basis of the interaction with eIF6 and provides a structural framework for further studies of ribosome-associated diseases and the role of the 60S subunit in the initiation of protein synthesis.     

Crystal structure of a complex between the catalytic and regulatory (RIalpha) subunits of PKA

The 2.0-angstrom structure of the cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) catalytic subunit bound to a deletion mutant of a regulatory subunit (RIalpha) defines a previously unidentified extended interface. The complex provides a molecular mechanism for inhibition of PKA and suggests how cAMP binding leads to activation. The interface defines the large lobe of the catalytic subunit as a stable scaffold where Tyr247 in the G helix and Trp196 in the phosphorylated activation loop serve as anchor points for binding RIalpha. These residues compete with cAMP for the phosphate binding cassette in RIalpha. In contrast to the catalytic subunit, RIalpha undergoes major conformational changes when the complex is compared with cAMP-bound RIalpha. The inhibitor sequence docks to the active site, whereas the linker, also disordered in free RIalpha, folds across the extended interface. The beta barrel of cAMP binding domain A, which is the docking site for cAMP, remains largely intact in the complex, whereas the helical subdomain undergoes major reorganization.     

A role for interaction of the RNA polymerase flap domain with the sigma subunit in promoter recognition

In bacteria, promoter recognition depends on the RNA polymerase sigma subunit, which combines with the catalytically proficient RNA polymerase core to form the holoenzyme. The major class of bacterial promoters is defined by two conserved elements (the -10 and -35 elements, which are 10 and 35 nucleotides upstream of the initiation point, respectively) that are contacted by sigma in the holoenzyme. We show that recognition of promoters of this class depends on the "flexible flap" domain of the RNA polymerase beta subunit. The flap interacts with conserved region 4 of sigma and triggers a conformational change that moves region 4 into the correct position for interaction with the -35 element. Because the flexible flap is evolutionarily conserved, this domain may facilitate promoter recognition by specificity factors in eukaryotes as well.     

普通小麦胚乳谷蛋白亚基的遗传研究 高分子量谷蛋白亚基变异的多样性及其在F#-1的遗传行为

本文研究了70个普通小麦品种和4个烘烤品质优良的亲本与4个农艺亲本间配置的20个正反交F#-1,以及1个杂交小麦F#-1的胚乳高分子量谷蛋白亚基。发现它们在品种间的变异较大,在品种内是稳定和一致的。它们在杂种F#-1呈现共显性遗传和倾母现象。讨论了杂种F#-1胚乳高分子量谷蛋白亚基共显性遗传在杂种判断和品种纯度鉴定中的应用。     

Structural evidence for a two-metal-ion mechanism of group I intron splicing

We report the 3.4 angstrom crystal structure of a catalytically active group I intron splicing intermediate containing the complete intron, both exons, the scissile phosphate, and all of the functional groups implicated in catalytic metal ion coordination, including the 2'-OH of the terminal guanosine. This structure suggests that, like protein phosphoryltransferases, an RNA phosphoryltransferase can use a two-metal-ion mechanism. Two Mg2+ ions are positioned 3.9 angstroms apart and are directly coordinated by all six of the biochemically predicted ligands. The evolutionary convergence of RNA and protein active sites on the same inorganic architecture highlights the intrinsic chemical capacity of the two-metal-ion catalytic mechanism for phosphoryl transfer.     

Reversing the inactivation of peroxiredoxins caused by cysteine sulfinic acid formation

The active-site cysteine of peroxiredoxins is selectively oxidized to cysteine sulfinic acid during catalysis, which leads to inactivation of peroxidase activity. This oxidation was thought to be irreversible. However, by metabolic labeling of mammalian cells with 35S, we show that the sulfinic form of peroxiredoxin I, produced during the exposure of cells to H2O2, is rapidly reduced to the catalytically active thiol form. The mammalian cells' ability to reduce protein sulfinic acid might serve as a mechanism to repair oxidatively damaged proteins or represent a new type of cyclic modification by which the function of various proteins is regulated.     

Structure of a peptide inhibitor bound to the catalytic subunit of cyclic adenosine monophosphate-dependent protein kinase

The structure of a 20-amino acid peptide inhibitor bound to the catalytic subunit of cyclic AMP-dependent protein kinase, and its interactions with the enzyme, are described. The x-ray crystal structure of the complex is the basis of the analysis. The peptide inhibitor, derived from a naturally occurring heat-stable protein kinase inhibitor, contains an amphipathic helix that is followed by a turn and an extended conformation. The extended region occupies the cleft between the two lobes of the enzyme and contains a five-residue consensus recognition sequence common to all substrates and peptide inhibitors of the catalytic subunit. The helical portion of the peptide binds to a hydrophobic groove and conveys high affinity binding. Loops from both domains converge at the active site and contribute to a network of conserved residues at the sites of magnesium adenosine triphosphate binding and catalysis. Amino acids associated with peptide recognition, nonconserved, extend over a large surface area.     

相同遗传背景下7和7+8亚基对小麦品质的影响

 高分子量麦谷蛋白与小麦品质的关系十分密切。但分析结果往往因所用材料而有差异,主要是不能消除不同遗传背景的影响。春小麦品种高原602所含高分子量麦谷蛋白亚基为Null,7和2+11,永良12号所含高分子量麦谷蛋白亚基为Null,7+8和2+11,二者差异仅在于Glu-B1位点的高分子量麦谷蛋白亚基不同,即永良12号比高原602多了个8亚基。用高原602和永良12号分别按正、反交组合进行杂交,在杂种F₃代,选择只有7亚基和7+8亚基差异的单株,在遗传背景相似的条件下,研究7和7+8亚基对小麦品质的影响。结果表明：7亚基和7+8亚基两组籽粒各项品质指标的t测验结果均不显著,说明7亚基和7+8亚基对小麦品质的影响无明显差异,即8亚基的有无对7亚基的作用无明显影响。     

杂交水稻寻杂29种子蛋白质组分的研究

 本研究用十二烷基硫酸钠聚丙烯酰胺凝胶电泳(SDS-PAGE)分析寻杂29单粒种子中清蛋白、球蛋白、醇溶蛋白和谷蛋白的亚基组成.SDS-PAGE表明,没有巯基乙醇(ME)时,谷蛋白以二硫键连接亚基呈高分子量形式存在.寻杂29和常规品种云-1比较,谷蛋白在溶解性,结构方面存在差异.寻杂29与其三系亲本,以及云-1比较,它们的种子盐溶蛋白在多肽组成和含量上存在明显差异.水稻种子盐溶蛋白的差异可考虑作为种子纯度判断的指标.     

小麦远缘杂交后代的高分子量麦谷蛋白亚基组成分析

[目的]为杂种后代的选择和品质育种提供参考依据。[方法]以P5和郑州9023远缘杂交F2代株系为试材,用十二烷基磺酸钠-聚丙烯酰胺凝胶电泳法鉴定分析了杂交后代的高分子量麦谷蛋白亚基组成。[结果]在Glu-A1,Glu-B1和Glu-D1 3个位点上分别均检测到2种亚基类型,3位点结合共出现2种组成类型。其中,在Glu-A1位点上,1种亚基出现频率最高,为66.7%;在Glu-B1位点上出现了7和7+8亚基,后者所占的比例是66.7%;Glu-D1位点上出现了2+12亚基和被世界公认的优质亚基5+10,其中,5+10亚基出现频率高达66.7%。杂交后代平均品质评分高达8分,两个株系的品质评分达到了10分。[结论]该杂交获得的这些携带优良亚基的材料可以作为优质面包小麦新品种或育种材料使用,是栽培小麦品质改良的极好新种质资源。     

一粒葡8-5-2和P5小麦杂交后代种子贮藏蛋白分析

[目的]探明优质小麦杂交后代的种子贮藏蛋白组成变化。[方法]采用SDS-PAGE分析2个亲本小麦株系一粒葡8-5-2和P5及其杂交F3株系的高分子量（HMW）谷蛋白组成,并对谷蛋白亚基评分;采用A-PAGE方法分析醇溶蛋白谱带。[结果]杂交后代株系中共出现4种HMW谷蛋白亚基组合类型,优质亚基及亚基组合所占的比例较多,其中Glu-A1位点1亚基出现频率为77.8%、Glu-D1位点5＋10亚基出现频率高达89.9%,杂交后代平均品质评分高达8分。A-PAGE方法分析表明,在醇溶蛋白谱带中,供试F3株系在ω区域出现3种变异,在γ、β、α3个区域变化不明显。[结论]该研究为增加杂种后代选择的准确性和提高品质育种效率提供了重要参考。