Specific incorporation of cyclophilin A into HIV-1 virions

Abstract

Little is known about host factors necessary for retroviral virion assembly or uncoating. We have previously shown that the principal structural protein of the human immunodeficiency virus HIV-1, the Gag polyprotein, binds the cyclophilin peptidyl-prolyl isomerases; cyclophilins catalyse a rate-limiting step in protein folding and protect cells from heat shock. Here we demonstrate that cyclophilin A is specifically incorporated into HIV-1 virions but not into virions of other primate immunodeficiency viruses. A proline-rich region conserved in all HIV-1 Gag polyproteins is required for cyclophilin A binding and incorporation. Disruption of a single proline blocks the Gag-cyclophilin interaction in vitro, prevents cyclophilin A incorporation into virions, and inhibits HIV-1 replication. Our results indicate that the interaction of Gag with cyclophilin A is necessary for the formation of infectious HIV-1 virions.

Extended binding sites of cyclophilin as revealed by the interaction with HIV‐1 Gag polyprotein derived oligopeptides

“…The Pro 222 residue that was found to be critical in a genetic screen [16] was invariantly positioned in peptides 1-5. Obviously, by a knowledge-based model the heptapeptide 1 already fulfils the structural requirements to act as an alternative substrate within a Cypl8 assay.…”

“…Incorporation of Cypl8 into HIV-1 virions occurred via contact with a proline-rich segment of the capsid domain of Pr55 g~g [16]. This conserved array totalling four prolines occurs in the periodicity (P(X)4p~22(X)2P(X)sP).…”

“…Mutant proteins of the HIV-1HxB2, having site-directed mutations, P222A or G221A, failed to bind on GST-CypI8. Virions equipped with these proteins cannot sequester Cypl8 into the released virions [15,16], emphasizing the importance of the Gly221-Pro 222 bond for Pr55g'~g/Cyp18 complex formation. With respect to Cypl8 packaging, P225A behaves like wild type devoid of forming a defective viral phenotype.…”

NMR reveals novel mechanisms of protein activity regulation

“…Proline cis-trans isomerization has emerged as a particularly efficient regulatory mechanism in many biological processes, including cell signaling, [62][63][64][65] neurodegeneration, 66 amyloidogenesis, 67 channel gating, 68 gene regulation, 69,70 phage and virus infection, 71,72 enzyme function, 73,74 and ligand recognition. 75 Proline isomerization is unique in that it exerts its function through multiple mechanisms involving (i) significant conformational changes caused by the 180 rotation about the prolyl bond, (ii) slow kinetics of isomerization affording a molecular timer, and (iii) the recruitment of prolyl cis-trans isomerase enzymes (PPIases).…”

CD147 stimulates HIV-1 infection in a signal-independent fashion

“…This notion has been supported in a number of subsequent publications [14][15][16]. CypA is incorporated into HIV-1 particles during virus morphogenesis through a specific interaction with the CA domain of the Gag precursor polyprotein [17][18][19][20] and plays an essential role in the early steps of the HIV-1 life cycle [21;22]. Biochemical studies indicate that CypA is exposed on the viral surface [23;24] and thus may signal through CD147.…”