2006年人禽流感H_5N_1毒株PA基因特性、变异和进化

目的通过对人禽流感H5N1毒株PA基因序列的变异分析,揭示毒株PA基因特征、变异与进化。方法检测广东地区人禽流感H5N1毒株PA基因核苷酸序列,同时检索全球人禽流感H5N1毒株PA基因序列,采用MEGA4.0软件对检索的人禽流感H5N1毒株PA基因核苷酸序列进行比对和分析;并结合流行病学资料对变异毒株进行进化速度分析。结果PA蛋白呈酸性,等电点pH5.4。1997-2006年52株毒株PA基因核苷酸序列同源性分成两组,1997年毒株为第一组(G1),2003-2006年香港、越南、泰国、印尼、中国大陆毒株、土耳其、伊拉克、阿塞拜疆、埃及毒株为第二组(G2)。PA基因114个氨基酸位点置换,占15.9(114/716),其中2003-2006年毒株PA基因有17个氨基酸位点不同于1997年毒株。PA基因Ks值为30.9×10-6～46.1×10-6Nt/d,Ka值为4.50×10-6～8.13×10-6Nt/d;而PA基因的同义突变速度是错义突变速度的5.7～6.9倍,显示PA基因受到机体免疫压力较小;检验发现PA基因进化存在负选择性压力。PA基因中潜在的7个糖基化位点基本稳定,毒株IDNS-569H-06的PA基因半胱氨酸发生置换(S224C)。结论PA基因进化分成两系列,PA基因进化特点是自发突变较快,而受到机体免疫机制压力较小;A基因与其它多聚酶基因(PB2和PB1)比较,核苷酸序列同源性和进化在时间特征和地区特征方面具有一致性;来自中国大陆的毒株进化值得关注。人禽流感H5N1毒株PA基因在自然界变异频繁,可能影响HN毒株致病性和在人-人传播能力。

Characterization, variation and evolution of the polymerase a gene in human avian infleuenza virus H5N1 strain in 2006

The characterization,variation and evolution of the polymerase A(PA) gene in human avian infleuenza virus H5N1 strain were analyzed on its variation in nucleotide sequence and the amino acids encoded by this gene,in which the nucleotide sequence of the PA gene in human avian influenza viruses isolated from Guangdong province in 2006 was sequenced and the PA genes of the global strains were searched out from internet.The variations of these PA genes were analyzed by MEGA 4.0 software and their evolutionary speed was studied by means of epidemiological data.It was found that the PA protein appeared to be acidic with an isoelectric point of pH 5.4.The 52 strains of virus with PA genes isolated from 1997 to 2006 could be divided into two groups according to their homology in nucleotide sequences,in which the strain isolated from Hongkong in 1997 belonged to the first group(G1),while those isolated from Vietnam,Thailand,Indonesia,China mainland,Turkey,Iraq,Azerbaijan and Egypt during 2003-2006 were included in the second group(G2).There were 114 substitutions on amino acid loci in PA genes of all strains,accounting to 15.9%(114/716),whereas there were 17 amino acid loci different from those strains isolated in 1997.In the synonymous variation,the Ks and Kavalues of the PA gene were 30.9×10-6-46.1×10-6 Nt/d and 4.50×10-6-8.13×10-6 Nt/d respectively.Meanwhile,the speed of the synonymous mutation were 5.7-6.9 times more rapid than those of the missense mutation,indicating that less human immunological pressure and the negative selective pressure existed as demonstrated by biological tests.The seven potential glycosylated domains in PA protein in strains isolated during 1997-2006 appeared to be considerably stable,except the cysteine substitution(S224C) occurring in the PA gene of strain IDNS-569H-06.From these observations,it is apparent that the PA gene of human avian influenza virus evolves rapidly in the spontaneous mutation,but shows less human immunological pressure.PA gene,in comparison with other polymerases of the virus,such as PB1 and PB2,its nucleotide sequence homology and the evolutionary characteristics in times and places were considerably consistent.The evolution of strains isolated in China mainland is worthy of further investigation,because the PA gene of human avian influenza virus strain H5H1 evolves rapidly in nature,which may have impact on the pathogenesis and the capacity of human to human transmission.