RESUMEN
The entry of human immunodeficiency virus (HIV-1) into cells is initiated by binding of the gp120 exterior envelope glycoprotein to the receptor, CD4. How does CD4 binding trigger conformational changes in gp120 that allow the gp41 transmembrane envelope glycoprotein to mediate viral-cell membrane fusion? The transition from the unliganded to the CD4-bound state is regulated by two potentially flexible topological layers (layers 1 and 2) in the gp120 inner domain. Both layers apparently contribute to the noncovalent association of unliganded gp120 with gp41. After CD4 makes initial contact with the gp120 outer domain, layer 1-layer 2 interactions strengthen gp120-CD4 binding by reducing the off rate. Layer 1-layer 2 interactions also destabilize the activated state induced on HIV-1 by treatment with soluble CD4. Thus, despite lack of contact with CD4, the gp120 inner-domain layers govern CD4 triggering by participating in conformational transitions within gp120 and regulating the interaction with gp41.
Asunto(s)
Antígenos CD4/metabolismo , Proteína gp120 de Envoltorio del VIH/metabolismo , Proteína gp41 de Envoltorio del VIH/metabolismo , VIH-1/metabolismo , Internalización del Virus , Animales , Antígenos CD4/genética , Perros , Genotipo , Proteína gp120 de Envoltorio del VIH/química , Proteína gp120 de Envoltorio del VIH/genética , Proteína gp41 de Envoltorio del VIH/química , Proteína gp41 de Envoltorio del VIH/genética , Proteasa del VIH/metabolismo , VIH-1/genética , VIH-1/inmunología , Células HeLa , Humanos , Ligandos , Modelos Moleculares , Mutación , Fenotipo , Unión Proteica , Conformación Proteica , Procesamiento Proteico-Postraduccional , Estructura Terciaria de Proteína , Receptores CCR5/metabolismo , Relación Estructura-Actividad , TransfecciónRESUMEN
Nonnative disulfide bond formation can play a critical role in the assembly of disulfide bonded proteins. During the folding and assembly of the P22 tailspike protein, nonnative disulfide bonds form both in vivo and in vitro. However, the mechanism and identity of cysteine disulfide pairs remains elusive, particularly for P22 tailspike, which contains no disulfide bonds in its native, functional form. Understanding the interactions between cysteine residues is important for developing a mechanistic model for the role of nonnative cysteines in P22 tailspike assembly. Prior in vivo studies have suggested that cysteines 496, 613, and 635 are the most likely site for sulfhydryl reactivity. Here we demonstrate that these three cysteines are critical for efficient assembly of tailspike trimers, and that interactions between cysteine pairs lead to productive assembly of native tailspike.