Functional redundancy in HIV-1 particle assembly

Tuesday, October 09, 2012 — Poster Session I
1:00 p.m. – 3:00 p.m	Natcher Conference Center, Building 45	NCI	VIROL-12

* FARE Award Winner

Authors

• I.P. O'Carroll
• R.M. Crist
• J. Mirro
• D. Harvin
• F. Soheilian
• A. Kamata
• K. Nagashima
• A. Rein

Abstract

HIV-1 particle assembly is a potential therapeutic target. The retroviral particle building block is the Gag protein which consists of three domains: 1) the matrix (MA), which binds the plasma membrane; 2) the capsid (CA), involved in inter-protein interactions; and 3) the nucleocapsid (NC), the main RNA-binding domain. Nucleic acid is required for Gag molecules to assemble in vitro. Several studies have suggested that RNA contributes to assembly by promoting Gag oligomerization. However, in vivo, deletion of the NC domain does not disable particle formation. We have analyzed the content of HIV particles formed in the absence of NC and found that they are virtually devoid of RNA. To understand how HIV-1 assembles in vivo independently of RNA, we designed several mutants that disrupt: i) the Gag dimer interface on the CA domain, ii) Gag-membrane interactions, or iii) NC-RNA interactions. We found that disruption of any one type of interaction is not sufficient to disable assembly; however, combination of any two mutants completely abolishes normal particle formation. We propose that, in vivo, HIV-1 Gag molecules come together into oligomers in several, functionally redundant ways: cooperative binding to nucleic acid; direct CA-CA interactions; and Gag-membrane interactions, which increase local Gag concentration.

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