Formation of a Human Immunodeficiency Virus Type 1 Core of Optimal Stability Is Crucial for Viral Replication

Abstract

Virions of human immunodeficiency virus type 1 (HIV-1) and other lentiviruses contain conical cores consisting of a protein shell composed of the viral capsid protein (CA) surrounding an internal viral ribonucleoprotein complex. Although genetic studies have implicated CA in both early and late stages of the virus replication cycle, the mechanism of core disassembly following penetration of target cells remains undefined. Using quantitative assays for analyzing HIV-1 core stability in vitro, we identified point mutations in CA that either reduce or increase the stability of the HIV-1 core without impairing conical core formation in virions. Alterations in core stability resulted in severely attenuated HIV-1 replication and impaired reverse transcription in target cells with only minimal effects on viral DNA synthesis in permeabilized virions in vitro. We conclude that formation of a viral core of optimal stability is a prerequisite for efficient HIV-1 infection and suggest that disassembly of the HIV-1 core is a regulated step in infection that may be an attractive target for pharmacologic intervention

Specific recognition and accelerated uncoating of retroviral capsids by the TRIM5α restriction factor

“…These results suggest that the intracellular particulate capsids detected in our assay exhibit densities between those of 45% sucrose (1.20 g͞ml) and 55% sucrose (1.26 g͞ml), a result that is in good agreement with previous estimates of the density of cores (1.24 -1.26 g͞ml) prepared by detergent treatment of HIV-1 virions (29,41,43). These results are also consistent with the expectation that much of the capsid protein nonspecifically taken into cells is trapped in endosomes or lysosomes, which have reported densities of Ͻ1.20 g͞ml (40,42).…”

“…The uncoating of the HIV-1 capsid is thought to precede reverse transcription, whereas MLV capsid proteins remain associated with the reverse transcription and preintegration complexes (25)(26)(27)(28). The study of HIV-1 capsid mutants suggests that capsid uncoating may be a temporally regulated process, with either too rapid or too slow disassembly compromising virus infectivity (29). Host cell factors involved in uncoating are unknown (21,30,31).…”

Binding and Susceptibility to Postentry Restriction Factors in Monkey Cells Are Specified by Distinct Regions of the Human Immunodeficiency Virus Type 1 Capsid

“…It is also possible that these mutants exhibit more capsid stability and are therefore more available to compete for the restriction factor(s). The high degree of replication competence of these mutants suggests that such changes in capsid stability, if present, must be subtle, as large positive or negative changes in this parameter have been reported to be detrimental to viral infectivity (18).…”

The structural biology of HIV assembly

“…Genetic analyses indicate that properly assembled capsids are required for the successful completion of reverse transcription (and other early events) [47,49,50,67,71,129,130] and also for later events that accompany nuclear localization of the preintegration complex [130,131]. Moreover, mutations that either increase or decrease capsid stability can reduce viral infectivity, suggesting that the timing (or extent) of capsid disassembly is probably important for successful completion of the first half of the viral life cycle [129].…”