Type I and type II GABAA-benzodiazepine receptors produced in transfected cells

GABAA (gamma-aminobutyric acid A)-benzodiazepine receptors expressed in mammalian cells and assembled from one of three different alpha subunit variants (alpha 1, alpha 2, or alpha 3) in combination with a beta 1 and a gamma 2 subunit display the pharmacological properties of either type I or type II receptor subtypes. These receptors contain high-affinity binding sites for benzodiazepines. However, CL 218 872, 2-oxoquazepam, and methyl beta-carboline-3-carboxylate (beta-CCM) show a temperature-modulated selectivity for alpha 1 subunit-containing receptors. There were no significant differences in the binding of clonazepam, diazepam, Ro 15-1788, or dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) to all three recombinant receptors. Receptors containing the alpha 3 subunit show greater GABA potentiation of benzodiazepine binding than receptors containing the alpha 1 or alpha 2 subunit, indicating that there are subtypes within the type II class. Thus, diversity in benzodiazepine pharmacology is generated by heterogeneity of the alpha subunit of the GABAA receptor.     

Resolution of a signal transfer region from a general binding domain in gbeta for stimulation of phospholipase C-beta2

Signaling by guanine nucleotide-binding proteins (G proteins) involves sequential protein-protein interactions. G protein-betagamma subunit (Gbetagamma) interactions with phospholipase C-beta2 (PLC-beta2) were studied to determine if all Gbeta contacts are required for signaling. A peptide encoding Gbeta amino acid residues 86 to 105 stimulated PLC-beta2. Six residues (96 to 101) within this sequence could transfer signals and thus constitute a core signal transfer region. Another peptide, encoding Gbeta amino acid residues 115 to 135, did not substantially stimulate PLC-beta2 by itself but inhibited Gbetagamma stimulation, indicating that residues 115 to 135 constitute a general binding domain. Resolution of signal transfer regions from general binding domains indicates that all protein-protein contacts are not required for signal transfer and that it may be feasible to synthesize agonists and antagonists that regulate intracellular signal flow.     

A single receptor binds both insulin-like growth factor II and mannose-6-phosphate

Amino acid sequences deduced from rat complementary DNA clones encoding the insulin-like growth factor II (IGF-II) receptor closely resemble those of the bovine cation-independent mannose-6-phosphate receptor (Man-6-P receptorCI), suggesting they are identical structures. It is also shown that IGF-II receptors are adsorbed by immobilized pentamannosyl-6-phosphate and are specifically eluted with Man-6-P. Furthermore, Man-6-P specifically increases by about two times the apparent affinity of the purified rat placental receptor for 125I-labeled IGF-II. These results indicate that the type II IGF receptor contains cooperative, high-affinity binding sites for both IGF-II and Man-6-P-containing proteins.     

Nucleotide control of interdomain interactions in the conformational reaction cycle of SecA

The SecA adenosine triphosphatase (ATPase) mediates extrusion of the amino termini of secreted proteins from the eubacterial cytosol based on cycles of reversible binding to the SecYEG translocon. We have determined the crystal structure of SecA with and without magnesium-adenosine diphosphate bound to the high-affinity ATPase site at 3.0 and 2.7 angstrom resolution, respectively. Candidate sites for preprotein binding are located on a surface containing the SecA epitopes exposed to the periplasm upon binding to SecYEG and are thus positioned to deliver preprotein to SecYEG. Comparisons with structurally related ATPases, including superfamily I and II ATP-dependent helicases, suggest that the interaction geometry of the tandem motor domains in SecA is modulated by nucleotide binding, which is shown by fluorescence anisotropy experiments to reverse an endothermic domain-dissociation reaction hypothesized to gate binding to SecYEG.     

High-throughput identification of catalytic redox-active cysteine residues

Cysteine (Cys) residues often play critical roles in proteins; however, identification of their specific functions has been limited to case-by-case experimental approaches. We developed a procedure for high-throughput identification of catalytic redox-active Cys in proteins by searching for sporadic selenocysteine-Cys pairs in sequence databases. This method is independent of protein family, structure, and taxon. We used it to selectively detect the majority of known proteins with redox-active Cys and to make additional predictions, one of which was verified. Rapid accumulation of sequence information from genomic and metagenomic projects should allow detection of many additional oxidoreductase families as well as identification of redox-active Cys in these proteins.     

可结合Caco-2细胞表面蛋白的副溶血弧菌外膜蛋白的筛选与鉴定

[目的]筛选可结合Caco-2细胞表面蛋白的副溶血弧菌外膜蛋白。[方法]筛选副溶血弧菌外膜中的黏附蛋白,将Caco-2细胞表面蛋白生物素化并固定于中性卵白素树脂上,进一步利用亲和层析技术来筛选副溶血弧菌的外膜蛋白。[结果]通过LC-MS/MS质谱技术鉴定出3个候选蛋白:ATP synthase subunit alpha、ATP synthase subunit beta和outer membrane protein U。通过对这3个蛋白进行克隆基因和原核表达,成功纯化得到相应重组蛋白。通过进一步的间接免疫荧光试验,发现3种蛋白对于Caco-2细胞均有黏附作用。[结论]推测ATP synthase subunit alpha、ATP synthase subunit beta和outer membrane protein U这3种蛋白可能是潜在的黏附因子。     

A beta 3 integrin mutation abolishes ligand binding and alters divalent cation-dependent conformation

The ligand-binding function of integrin adhesion receptors depends on divalent cations. A mutant alpha IIb beta 3 integrin (platelet gpIIb/IIIa) that lacks ligand recognition shows immunologic evidence of a perturbed interaction with divalent cations. This was found to be caused by a G----T mutation that resulted in an Asp119----Tyr119 substitution in the beta 3 subunit. This residue is proximal to bound ligand and is in a conserved region among integrins that are enriched in oxygenated residues. The spacing of these residues aligns with the calcium-binding residues in EF hand proteins, suggesting interaction with receptor-bound divalent cation as a mechanism of ligand binding common to all integrins.     

A mercury-catalyzed, high-yield system for the oxidation of methane to methanol

A homogeneous system for the selective, catalytic oxidation of methane to methanol via methyl bisulfate is reported. The net reaction catalyzed by mercuric ions, Hg(II), is the oxidation of methane by concentrated sulfuric acid to produce methyl bisulfate, water, and sulfur dioxide. The reaction is efficient. At a methane conversion of 50 percent, 85 percent selectivity to methyl bisulfate ( approximately 43 percent yield; the major side product is carbon dioxide) was achieved at a molar productivity of 10(-7) mole per cubic centimeter per second and Hg(II) turnover frequency of 10(-3) per second. Separate hydrolysis of methyl bisulfate and reoxidation of the sulfur dioxide with air provides a potentially practical scheme for the oxidation of methane to methanol with molecular oxygen. The primary steps of the Hg(II)-catalyzed reaction were individually examined and the essential elements of the mechanism were identified. The Hg(II) ion reacts with methane by an electrophilic displacement mechanism to produce an observable species, CH(3)HgOSO(3)H, 1. Under the reaction conditions, 1 readily decomposes to CH(3)OSO(3)H and the reduced mercurous species, Hg(2)(2+) The catalytic cycle is completed by the reoxidation of Hg(2)(2+) with H(2)SO(4) to regenerate Hg(II) and byproducts SO(2) and H(2)O. Thallium(III), palladium(II), and the cations of platinum and gold also oxidize methane to methyl bisulfate in sulfuric acid.     

A G protein gamma subunit shares homology with ras proteins

Guanine nucleotide binding proteins (G proteins) that transduce signals from cell surface receptors to effector molecules are made up of three subunits, alpha, beta, and gamma. A complementary DNA clone that encodes a 71-amino acid protein was isolated from bovine brain; this protein contains peptide sequences that were derived from the purified gamma subunit of Gi and Go. The primary sequence of this G protein gamma subunit (G gamma) has 55 percent homology to the gamma subunit of transducin (T gamma) and also has homology to functional domains of mammalian ras proteins. The probe for isolating the clone was generated with the use of the polymerase chain reaction (PCR). The extent of divergence between T gamma and G gamma, the isolation of homologous PCR-generated fragments, and the differences between the predicted amino acid sequence of G gamma and that derived from the gamma subunit of Gi and Go indicate that gamma subunits are encoded by a family of genes.     

硝化还原假单胞菌SPQ03 PnSoxRS调控子的克隆和功能初步分析

从对百草枯具有高度抗性的硝化还原假单胞菌(Pseudomonas nitroreducens)菌株SPQ03中分离了PnSoxR和PnSoxS调控子.ScanProsite程序分析结果表明,SoxR氨基端含有一个MerR家族特有的DNA结合域,羧基端含有4个半胱氨酸残基,是MerR家族成员之一;SoxS是AraC家族成员,含有2个典型的AraC-HTH保守域;PnSoxR所编码的氨基酸与大肠杆菌SoxR的一致性为98%,而与同属的铜绿假单胞菌(Pseudomonas aeruginos)SoxR的一致性仅为56%,PnSoxR与大肠杆菌SoxS的一致性为100%,铜绿假单胞菌中没有发现SoxR基因存在.将PnSoxR和PnSoxS分别转化E.coli BL21,发现PnSoxS能赋予BL21百草枯(Paraquat)抗性.     

Calcium-induced movement of troponin-I relative to actin in skeletal muscle thin filaments

The role of troponin-I (the inhibitory subunit of troponin) in the regulation by Ca2+ of skeletal muscle contraction was investigated with resonance energy transfer and photo cross-linking techniques. The effect of Ca2+ on the proximity of troponin-I to actin in reconstituted rabbit skeletal thin filaments was determined. The distance between the cysteine residue at position 133 (Cys133) of troponin-I and Cys374 of actin increases by approximately 15 angstroms on binding of Ca2+ to troponin-C. Also, troponin-I labeled at Cys133 with benzophenone-4-maleimide could be photo cross-linked to actin in the absence of Ca2+, but not in its presence. These results suggest that troponin-I is attached to actin in the Ca2(+)-free or relaxed state of muscle, and that it detaches from actin on Ca2+ activation of contraction. Thus, troponin-I may function as a Ca2(+)-dependent molecular switch in regulation of skeletal muscle contraction.     

Evidence that the M2 membrane-spanning region lines the ion channel pore of the nicotinic receptor

Site-directed mutagenesis and expression in Xenopus oocytes were used to study acetylcholine receptors in which serine residues (i) were replaced by alanines (alpha, delta subunits) or (ii) replaced a phenylalanine (beta subunit) at a postulated polar site within the M2 transmembrane helix. As the number of serines decreased, there were decreases in the residence time and consequently the equilibrium binding affinity of QX-222, a quaternary ammonium anesthetic derivative thought to bind within the open channel. Receptors with three serine-to-alanine mutations also displayed a selective decrease in outward single-channel currents. Both the direction of this rectification and the voltage dependence of QX-222 blockade suggest that the residues mutated are within the aqueous pore of the receptor and near its cytoplasmic (inner) surface.     

Crystal structure of the ribosome at 5.5 A resolution

We describe the crystal structure of the complete Thermus thermophilus 70S ribosome containing bound messenger RNA and transfer RNAs (tRNAs) at 5.5 angstrom resolution. All of the 16S, 23S, and 5S ribosomal RNA (rRNA) chains, the A-, P-, and E-site tRNAs, and most of the ribosomal proteins can be fitted to the electron density map. The core of the interface between the 30S small subunit and the 50S large subunit, where the tRNA substrates are bound, is dominated by RNA, with proteins located mainly at the periphery, consistent with ribosomal function being based on rRNA. In each of the three tRNA binding sites, the ribosome contacts all of the major elements of tRNA, providing an explanation for the conservation of tRNA structure. The tRNAs are closely juxtaposed with the intersubunit bridges, in a way that suggests coupling of the 20 to 50 angstrom movements associated with tRNA translocation with intersubunit movement.     

小麦avenin-like的克隆、原核表达与品质效应研究

【目的】研究普通小麦不同品种的类燕麦贮藏蛋白（avenin-like）基因序列的多样性及其表达产物的加工品质效应。【方法】利用特异性引物对来源于不同地区的12个小麦品种（系）进行PCR扩增、克隆、测序及序列分析;构建JN542444原核表达载体后转入表达菌株Escherichia coli Rosetta gami B(DE3),IPTG诱导融合蛋白表达,并通过His-Trap HP柱纯化蛋白后进行微量掺粉试验。【结果】克隆获得22条avenin-like新基因序列（GenBank登录号JN542443-JN542464）,长度均为855 bp,且均具有可编码284个氨基酸残基的完整的开放阅读框,无内含子;半胱氨酸数目及位置相对保守,除JN542452含有17个Cys外,其余avenin-like所编码的蛋白质序列均含有18个Cys,且位置相同,预测可能形成7个分子内二硫键和4个分子间二硫键;发现3条罕见的avenin-like假基因（JN542448、JN542455和JN542456）,均因终止密码子的提前出现引起基因沉默;7份小麦品种共享一条avenin-like亚基,并与GenBank中来自普通小麦的HM027636完全一致,暂将该亚基命名为“Avenin-likeⅠ”;系统演化分析表明avenin-like编码蛋白与LMW-GS关系最近,与ω-gliadin的亲缘关系最远;SDS-PAGE检测融合蛋白成功表达,对纯化蛋白进行微量掺粉试验,发现Avenin-likeⅠ型蛋白亚基对小麦加工品质具有显著的正向效应。【结论】avenin-like在供试小麦品种中具有很低的多态性,且Avenin-likeⅠ型亚基能提高面粉加工品质。     

Sequence of the alpha subunit of photoreceptor G protein: homologies between transducin, ras, and elongation factors

A bovine retinal complementary DNA clone encoding the alpha subunit of transducin (T alpha) was isolated with the use of synthetic oligodeoxynucleotides as probes, and the complete nucleotide sequence of the insert was determined. THe predicted protein sequence of 354 amino acids includes the known sequences of four tryptic peptides and sequences adjacent to the residues that undergo adenosine diphosphate ribosylation by cholera toxin and pertussis toxin. On the basis of homologies to other proteins, such as the elongation factors of protein synthesis and the ras oncogene proteins, regions are identified that are predicted to be acylated and involved in guanine nucleotide binding and hydrolysis. Amino acid sequence similarity between T alpha and ras is confined to these regions of the molecules.     

A structural framework for deciphering the link between I-Ag7 and autoimmune diabetes

Susceptibility to murine and human insulin-dependent diabetes mellitus correlates strongly with major histocompatibility complex (MHC) class II I-A or HLA-DQ alleles that lack an aspartic acid at position beta57. I-Ag7 lacks this aspartate and is the only class II allele expressed by the nonobese diabetic mouse. The crystal structure of I-Ag7 was determined at 2.6 angstrom resolution as a complex with a high-affinity peptide from the autoantigen glutamic acid decarboxylase (GAD) 65. I-Ag7 has a substantially wider peptide-binding groove around beta57, which accounts for distinct peptide preferences compared with other MHC class II alleles. Loss of Asp(beta57) leads to an oxyanion hole in I-Ag7 that can be filled by peptide carboxyl residues or, perhaps, through interaction with the T cell receptor.     

Reexamination of the Three-Dimensional Structure of the Small Subunit of RuBisCo from Higher Plants

The structure of L(8)S(8) RuBisCo (where L is the large subunit and S is the small subunit) from spinach has been determined to a resolution of 2.8 ?ngstrom by using fourfold averaging of an isomorphous electron density map based on three heavy-atom derivatives. The structure of the S subunit is different from that previously reported for the tobacco S subunit in spite of 75 percent sequence identity. The elements of secondary structure, four antiparallel beta strands and two alpha helices, are the same, but the topology and direction of the polypeptide chain through these elements differ completely. One of these models is clearly wrong. The spinach model has hydrophobic residues in the core between the alpha helices and beta sheet as well as conserved residues in the subunit interactions. The deletion of residues 49 to 62 that is present in the Anabaena sequence removes a loop region in the spinach model. The positions of three mercury atoms in the heavy-atom derivatives agree with the assignment of side chains in the spinach structure.     

High-resolution epitope mapping of hGH-receptor interactions by alanine-scanning mutagenesis

A strategy, called alanine-scanning mutagenesis, was used to identify specific side chains in human growth hormone (hGH) that strongly modulate binding to the hGH receptor cloned from human liver. Single alanine mutations (62 in total) were introduced at every residue contained within the three discontinuous segments of hGH (residues 2 to 19, 54 to 74, and 167 to 191) that have been implicated in receptor recognition. The alanine scan revealed a cluster of a dozen large side chains that when mutated to alanine each showed more than a four times lower binding affinity to the hGH receptor. Many of these residues that promote binding to the hGH receptor are altered in homologs of hGH (such as placental lactogens and prolactins) that do not bind tightly to the hGH receptor. The overall folding of these mutant proteins was indistinguishable from that of the wild-type hGH, as determined by strong cross-reactivities with seven different conformationally sensitive monoclonal antibodies. The alanine scan also identified at least one side chain, Glu174, that hindered binding because when it was mutated to alanine the receptor affinity increased by more than a factor of four.     

Functional Characteristics of a Novel Chemosensory Protein in the Cotton Bollworm Helicoverpa armigera (Hübner)

A chemosensory protein named HarmCSP5 in cotton bollworm Helicoverpa armigera (Hübner) was obtained from antennal cDNA libraries and expressed in Escherichia coli. The real time quantitative PCR (RT-qPCR) results indicated that HarmCSP5 gene was mainly expressed in male and female antennae but also expressed in female legs and wings. Competitive binding assays were performed to test the binding affinity of recombinant HarmCSP5 to 60 odor molecules including some cotton volatiles. The resules showed that HarmCSP5 showed strong binding abilities to 4-ehtylbenzaldehyde and 3,4-dimethlbenz aldehyde, whereas methyl phenylacetate, 2-decanone, 1-pentanol, carvenol, isoborneol, nerolidol, 2-nonanone and ethyl heptanoate have relatively weak binding affinity. Moreover, the predicted 3D model of HarmCSP5 consists of six α-helices located among residues 33–38 (α1), 40–48 (α2), 62–72 (α3), 80–96 (α4), 98–108 (α5), and 116–119 (α6), two pairs of disulfide bridges Cys49-Cys55, Cys75-Cys78. The two amino acid residues, Ile94 and Trp101, may play crucial roles in HarmCSP5 binding with ligands and need further study for confirmation.