鸡传染性支气管炎病毒中国分离株LX4纤突蛋白基因分子特征

应用RT-PCR方法分别扩增了中国地方分离株IBV LX4 S1和S2基因并进行了基因的克隆和序列测定.结果发现,LX4 S基因由3495个核苷酸组成,编码一条1164个氨基酸残基组成的多肽.S基因编码产物裂解后形成的S1和S2亚单位分别由539和625个氨基酸残基组成.LX4 S基因推导氨基酸切割识别位点序列为HRRRR,与A2、SD/97/02和Z株相同,而与其它国内外参考毒株不同.与国内外10株已报道的具有全S基因序列的IBV参考毒株比较,LX4与国内分离毒株SD/97/02的核苷酸和氨基酸同源性最高.与32株国内外参考毒株的S1基因进化树分析比较表明,LX4与A2、SD/97/02、Z、TJ/96/02、JX/99/01和SAIBWJ等7个国内分离株在同一亚群内.在该亚群内,LX4与A2和SD/97/02亲缘关系更近,且三者在高变区和抗原表位均具有高度的同源性,而与本亚群内其它参考毒株对应的高变区和抗原表位同源性差异较大.LX4与H120 S1基因编码氨基酸的同源性虽然高于其它国外参考毒株,但同源性仍然较低,为75%.与参考毒株比较,LX4 S2基因的点突变造成其推导的氨基酸序列有11个位点发生改变,这些突变可能影响S2与S1蛋白之间的相互作用,从而影响S蛋白与特异性抗体的结合.

Molecular Characteristics of Spike Gene of Infectious Bronchitis Virus LX4 Isolated in China

S1 and S2 genes of IBV LX4 strain were amplified by RT PCR method.The two genes were cloned,sequenced and analyzed with the published genes of IBV strains.The results showed that the S gene of LX4 was composed of 3,495 mucleotides encoding for a polypeptide of 1,164 amino acids.The cleavage site sequence of S protein of LX4 contained five consecutive basic amino acids,His Arg Arg Arg Arg(HRRRR)and the deduced S1 and S2 proteins were composed of 539 and 625 amino acids respectively after S protein was cleaved.The result indicated that the low nucleotide identity of S1 gene between LX4 and H120 would be one of the reasons that caused infectious bronchitis disease in H120 immunized chickens.Meanwhile,we found that LX4 had closer relationship with the reference IBV strains that isolated in China.This phenomenon and the phylogenetic tree of S1 gene amino acid sequences indicated that they would have diverged from a common progenitor.Compared with reference strains that isolated in other countries,LX4 shared high identity with H120 at the level of amino acids.Meanwhile,this would be one of the other reasons that caused infectious bronchitis disease in H120 immunized chickens.