CagA蛋白序列可变区多态性分析

Polymorphism of Variable Regions of CagA Protein

背景:幽门螺杆菌(H.pylori)与胃十二指肠疾病关系密切。由于菌株之间CagAEPIYA基序数目及其间隔的氨基酸序列的不同,导致H.pylori主要毒力因子CagA蛋白的多态性和毒力差异。目前关于CagA蛋白多态性的研究缺乏系统性。目的:系统了解H.pyloriCagA蛋白序列多态性及其特征。方法:采用生物信息学软件序列比对分析与统计学软件数据加工整理技术相结合的方法,对NCBI、swiss_prot/tremble、DDBJ三大蛋白数据库CagA蛋白的97条全长序列和442条3’端部分序列进行多态性分析。结果:CagA蛋白氨基酸序列长短不等,主要是由可变区的变化引起的,可变区平均大小为(114.2±24.9)个氨基酸。539株H.pylori菌株CagA蛋白可变区EPIYA有14种突变型,占7.8%;EPIYA基序平均重复(3.3±0.7)次,最少1次,最多7次。两个EPIYA基序间的间隔序列主要有7种,其中R3C和R4C中的“FPLKRHDKVDELIKVG”以及R4C中的“TIDDLGGP”是西方株特征序列,R3D中的“KIASAGKGVGGFSGAG”和R4D中的“FPLRRSAAVNDLSKVG”、“TIDFDEAN”是东亚株特征序列。EPIYA及其间隔序列的不同组合构成了CagA可变区的17种不同类型。东亚株EPIYA基序重复次数显著少于西方株,而EPIYA-A、EPIYA-B位点数显著多于西方株。结论:CagA蛋白可变区呈现明显多态性,但有其内在规律;进一步研究CagA蛋白多态性与细菌毒力的关系可能揭示出更多H.pylori致病的分子生物学机制。

Background： Helicobacter pylori （H. pylori） is closely associated with gastroduodenal diseases. CagA protein is one of its most important virulence factor, of which the cytotoxins vary with the number of EPIYA motifs and interval sequences among different strains. But systematic study on the data on polymorphism of CagA protein of H. pylori remains few. Aims： To study systematically the sequence polymorphism and its characteristics of H. pylori CagA protein. Methods： CagA protein sequences were searched in NCBI, swiss_prot/tremble and DDBJ protein databases, complete sequences of 97 strains and 3＇ variable regions sequences of 442 strains of H. pylori were obtained, aligned and analyzed. Results： The number of amino acids of variable regions averaged 114.2±24.9 in 539 strains, which was the dominant causation inducing the polymorphism of CagA proteins. EPIYA motifs were repeated （3.3±0.7） times in average, seven times in the maximum and one time in the minimum in the variable regions; EPIYA motifs were found to have 14 kinds of mutant （7.8%）. With the exception of EPIYA motifs, there were seven sorts of interval sequences of the variable regions, among which ＂FPLKRHDKVDELIKVG＂ in R3C, R4C motifs and ＂TIDDLGGP＂ in R4C were the characteristic sequences of the Western-type strains, ＂KIASAGKGVGGFSGAG＂ in R3D and ＂FPLRRSAAVNDLSKVG＂, ＂TIDFDEAN＂ in R4D motifs were characteristic sequences of the East Asian-type strains. Because of the diversity in the sequence of EPIYA-A, -B, -C, -D sites, there were 17 kinds of different ABC-types and ABD-types in the variable regions of CagA proteins. EPIYA motifs repeat in the East Asian-type strains were significantly less, but EPIYA-A, EPIYA-B sites were significantly more than those in the Western-type strains. Conclusions： There exists diversity of the variable regions of CagA proteins, but with internal rules; further investigation on CagA proteins polymorphism and their relations to the virulence may uncover more molecular and biological mechanisms of H. pylori infection.