Role of Matrix in an Early Postentry Step in the Human Immunodeficiency Virus Type 1 Life Cycle

The matrix protein of human immunodeficiency virus type 1 (HIV-1) has been reported to play a crucial role in the targeting of the Gag polyprotein precursor to the plasma membrane and in the incorporation of viral envelope glycoproteins into budding virions. In this report, we present evidence that mutation of a highly conserved Leu at matrix amino acid 20 blocks or markedly delays virus replication in a range of cell types, including T-cell lines, primary human peripheral blood mononuclear cells, and monocyte-derived macrophages. These mutations do not impair virus assembly and release, RNA encapsidation, or envelope glycoprotein incorporation into virions but rather cause significant defects in an early step in the virus life cycle, as measured by single-cycle infectivity assays and the analysis of viral DNA synthesis early postinfection. This infectivity defect is independent of the type of envelope glycoprotein carried on mutant virions; similar results are obtained in pseudotyping experiments using wild-type or truncated HIV-1 envelope glycoproteins, the amphotropic murine leukemia virus envelope, or the vesicular stomatitis G protein. Intriguingly, matrix residue 20 mutations also increase the apparent binding of Gag to membrane, accelerate the kinetics of Gag processing, and induce defects in endogenous reverse transcriptase activity without affecting virion density or morphology. These results help elucidate the function of matrix in HIV-1 replication.

已有文献报道，人类免疫缺陷病毒1型（HIV-1）的基质蛋白（matrix protein）在将Gag多蛋白前体靶向转运至细胞质膜，以及将病毒包膜糖蛋白整合至出芽病毒粒子的过程中发挥关键作用。本研究提供证据显示，基质蛋白第20位高度保守的亮氨酸（Leu）发生突变后，会阻断或显著延缓病毒在多种细胞类型中的复制，这些细胞类型包括T细胞系、人类原代外周血单个核细胞以及单核细胞衍生的巨噬细胞。该类突变并不会损害病毒的组装与释放、RNA衣壳化，或是包膜糖蛋白向病毒粒子的整合；反而会在病毒生命周期的早期阶段引发显著缺陷，这一结论可通过单周期感染性试验以及感染早期的病毒DNA合成分析得到验证。此类感染性缺陷与突变病毒粒子所携带的包膜糖蛋白类型无关：在使用野生型或截短型HIV-1包膜糖蛋白、双嗜性鼠白血病病毒包膜，或是水疱性口炎病毒G蛋白进行的假型化实验中，均可得到相似的实验结果。值得注意的是，基质蛋白第20位的突变还会增强Gag与膜结构的表观结合能力，加速Gag的加工动力学过程，并在不影响病毒粒子密度与形态的前提下，引发内源性逆转录酶活性缺陷。上述研究结果有助于阐明基质蛋白在HIV-1复制过程中的功能。