Switch to Unusual Amino Acids at Codon 215 of the Human Immunodeficiency Virus Type 1 Reverse Transcriptase Gene in Seroconvertors Infected with Zidovudine-Resistant Variants

Sequences of the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) domain were determined by direct sequencing of HIV-1 RNA in successive plasma samples from eight seroconverting patients infected with virus bearing the T215Y/F amino acid substitution associated with zidovudine (ZDV) resistance. At baseline, additional mutations associated with ZDV resistance were detected. Three patients had the M41L amino acid change, which persisted. Two patients had both the D67N and the K70R amino acid substitutions; reversion to the wild type was seen at both positions in one of these patients and at codon 70 in the other one. Reversion to the wild type at codon 215 was observed in only one of eight patients. Unusual amino acids, such as aspartic acid (D) and cysteine (C), appeared at position 215 in four patients during follow-up. These variants isolated by coculturing were sensitive to ZDV. Overgrowth of these variants suggests that they have better fitness than the original T215Y variant. Intraindividual nucleoside substitutions over time were 10 times more frequent in codons associated with ZDV resistance (41, 67, 70, 215, and 219) than in other codons of the RT domain. The predominance of nonsynonymous substitutions observed over time suggests that most changes reflect adaptation of the RT function. The variance in sequence evolution observed among patients, in particular at codon 215, supports a role for chance in the evolution of the RT domain.

本研究对8名感染携带齐多夫定（zidovudine, ZDV）耐药相关T215Y/F氨基酸替换病毒的血清转换患者的连续血浆样本中的人类免疫缺陷病毒1型（human immunodeficiency virus type 1, HIV-1）RNA进行直接测序，获得了其逆转录酶（reverse transcriptase, RT）结构域的序列。基线样本中，研究人员检测到了其他与ZDV耐药相关的突变：3名患者存在M41L氨基酸改变且该突变持续存在；2名患者同时携带D67N与K70R氨基酸替换，其中1名患者的两个位点均回复为野生型，另1名患者仅在70号密码子处发生回复突变。8名患者中仅1名在215号密码子处观察到回复为野生型的现象。随访期间，4名患者的215号位点出现了天冬氨酸（aspartic acid, D）与半胱氨酸（cysteine, C）等非常规氨基酸。通过共培养分离得到的上述变异株对ZDV敏感，其过度增殖提示它们的适应性优于原始的T215Y变异株。随时间推移，RT结构域中与ZDV耐药相关的密码子（41、67、70、215及219）内的个体内核苷酸替换频率是其他密码子的10倍。研究观察到的非同义替换占优现象提示，多数序列变化反映了RT功能的适应性进化。不同患者间的序列演化存在差异，尤以215号密码子处为甚，这表明随机因素在RT结构域的演化过程中扮演了重要角色。