MOLECULAR NOVELTY AND CONSERVATION IN BACTERIAL PROTEIN SEQUENCES

从不同细菌的基因序列推导的蛋白质序列， 古细菌产生了大量关于蛋白质的新知识 功能、相互作用和进化。 研究了一些新的发现， 通过包括定向诱变的协同方法， 光谱/酶学分析和计算机序列分析 数据库。调查结果包括： A. 主要真核生物蛋白质家族的细菌同源物。 丝氨酸/苏氨酸蛋白激酶的细菌同系物进一步被发现。 在蓝细菌和古细菌中进行了研究。 这些显然是 与蛋白激酶C亚家族相对相似，但它们的 磷酸化特异性仍有待证实。 B。 谷氨酸脱氢酶中新的质子交换机制。 这 酶与其他NAD/NADP依赖性内切酶的不同之处在于缺乏 催化组氨酸残基。 从序列保守和 对E.大肠杆菌酶，与 共生梭菌酶的晶体结构，赖氨酸三联体 在活性位点中鉴定了残基。 这些具有新颖性 质子化性质，并明显地在二羧酸中协同作用 底物结合、铵的去质子化和其它质子交换 谷氨酸脱氢酶催化步骤。 C. 复杂细菌中的序列家族。 新序列来自 多细胞和分化细菌，链霉菌，粘球菌和 各种蓝藻和古细菌，调查了全球 数据库序列相似性搜索。 百分之50以上的普选 可分类的蛋白质序列在E.杆菌和 其他研究充分的肠道细菌，其中许多具有真核生物 同系物。 低复杂性区段和多个重复的实例是 出现的频率越来越高。 项目意义： 基因组序列从代谢和 形态发生多样的细菌继续提供丰富的， 具有成本效益的来源的新发现的分子功能和 蛋白质的进化

Protein sequences deduced from gene sequences of diverse bacteria and archaebacteria are yielding a wealth of new knowledge on protein functions, interactions and evolution. Some novel findings were studied by concerted methods including directed mutagenesis, spectroscopic/enzymological analyses and computer analyses of sequence databases. Findings include:- A. Bacterial homologs of major "eukaryotic" protein families. Bacterial homologs of Serine/Threonine protein kinases were further investigated in cyanobacteria and archaebacteria. These are evidently relatively similar to the protein kinase C subfamily, but their phosphorylation specificity remains to be confirmed. B. Novel proton exchange mechanism in glutamate dehydrogenase. This enzyme differs from other NAD/NADP dependent dehydrogenases in lacking a catalytic histidine residue. From sequence conservation and site-directed mutagenesis of the E. coli enzyme, in comparison with the crystal structure of the Clostridium symbiosum enzyme, a triad of lysine residues was identified in the active site. These have novel protonation properties and evidently act in concert in dicarboxylate substrate binding, deprotonation of ammonium and other proton exchange steps of glutamate dehydrogenase catalysis. C. Sequence families in complex bacteria. New sequences from multicellular and differentiating bacteria, Streptomyces, Myxococcus and various cyanobacteria and archaebacteria, were investigated by global database sequence similarity searches. More than 50 percent of the classifiable protein sequences did not have counterparts in E. coli and other well-studied enteric bacteria, and many of these had eukaryotic homologs. Examples of low-complexity segments and multiple repeats are emerging with increasing frequency. Significance of project: Genome sequences from metabolically and morphogenetically diverse bacteria continue to provide a rich and cost-effective source of new discoveries on the molecular functions and evolution of proteins.