Boyer Paul L, Sarafianos Stefan G, Clark Patrick K, Arnold Eddy, Hughes Stephen H
HIV Drug Resistance Program, NCI-Frederick, Maryland, USA.
PLoS Pathog. 2006 Feb;2(2):e10. doi: 10.1371/journal.ppat.0020010. Epub 2006 Feb 17.
The human immunodeficiency virus type 1 (HIV-1) develops resistance to all available drugs, including the nucleoside analog reverse transcriptase inhibitors (NRTIs) such as AZT. ATP-mediated excision underlies the most common form of HIV-1 resistance to AZT. However, clinical data suggest that when HIV-2 is challenged with AZT, it usually accumulates resistance mutations that cause AZT resistance by reduced incorporation of AZTTP rather than selective excision of AZTMP. We compared the properties of HIV-1 and HIV-2 reverse transcriptase (RT) in vitro. Although both RTs have similar levels of polymerase activity, HIV-1 RT more readily incorporates, and is more susceptible to, inhibition by AZTTP than is HIV-2 RT. Differences in the region around the polymerase active site could explain why HIV-2 RT incorporates AZTTP less efficiently than HIV-1 RT. HIV-1 RT is markedly more efficient at carrying out the excision reaction with ATP as the pyrophosphate donor than is HIV-2 RT. This suggests that HIV-1 RT has a better nascent ATP binding site than HIV-2 RT, making it easier for HIV-1 RT to develop a more effective ATP binding site by mutation. A comparison of HIV-1 and HIV-2 RT shows that there are numerous differences in the putative ATP binding sites that could explain why HIV-1 RT binds ATP more effectively. HIV-1 RT incorporates AZTTP more efficiently than does HIV-2 RT. However, HIV-1 RT is more efficient at ATP-mediated excision of AZTMP than is HIV-2 RT. Mutations in HIV-1 RT conferring AZT resistance tend to increase the efficiency of the ATP-mediated excision pathway, while mutations in HIV-2 RT conferring AZT resistance tend to increase the level of AZTTP exclusion from the polymerase active site. Thus, each RT usually chooses the pathway best suited to extend the properties of the respective wild-type enzymes.
1型人类免疫缺陷病毒（HIV-1）会对所有可用药物产生耐药性，包括齐多夫定（AZT）等核苷类似物逆转录酶抑制剂（NRTIs）。ATP介导的切除是HIV-1对AZT产生耐药性的最常见形式的基础。然而，临床数据表明，当HIV-2受到AZT挑战时，它通常会积累耐药性突变，这些突变通过减少三磷酸齐多夫定（AZTTP）的掺入而不是通过选择性切除单磷酸齐多夫定（AZTMP）来导致对AZT的耐药性。我们在体外比较了HIV-1和HIV-2逆转录酶（RT）的特性。尽管两种RT的聚合酶活性水平相似，但与HIV-2 RT相比，HIV-1 RT更容易掺入AZTTP，并且对AZTTP的抑制更敏感。聚合酶活性位点周围区域的差异可以解释为什么HIV-2 RT掺入AZTTP的效率低于HIV-1 RT。与HIV-2 RT相比，HIV-1 RT以ATP作为焦磷酸供体进行切除反应的效率明显更高。这表明HIV-1 RT比HIV-2 RT具有更好的新生ATP结合位点，使得HIV-1 RT更容易通过突变形成更有效的ATP结合位点。HIV-1和HIV-2 RT的比较表明，在假定的ATP结合位点存在许多差异，这可以解释为什么HIV-1 RT能更有效地结合ATP。HIV-1 RT掺入AZTTP的效率比HIV-2 RT更高。然而，HIV-1 RT在ATP介导的AZTMP切除方面比HIV-2 RT更有效。赋予AZT耐药性的HIV-1 RT突变往往会提高ATP介导的切除途径的效率，而赋予AZT耐药性的HIV-2 RT突变往往会增加AZTTP从聚合酶活性位点的排除水平。因此，每种RT通常会选择最适合扩展各自野生型酶特性的途径。
