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Structural basis for viral late-domain binding to Alix
http://www.nature.com/nsmb
Nature Publishing Group
200 7
Sangho Lee1, Anjali Joshi2, Kunio Nagashima3, Eric O Freed2 & James H Hurley1
The modular protein Alix is a central node in endosomal-lysosomal trafcking and the budding of human immunodeciency virus (HIV)-1. The Gag p6 protein of HIV-1 contains a LYPxnLxxL motif that is required for Alix-mediated budding and binds a region of Alix spanning residues 360702. The structure of this fragment of Alix has the shape of the letter V and is termed the V domain. The V domain has a topologically complex arrangement of 11 a-helices, with connecting loops that cross three times between the two arms of the V. The conserved residue Phe676 is at the center of a large hydrophobic pocket and is crucial for binding to a peptide model of HIV-1 p6. Overexpression of the V domain inhibits HIV-1 release from cells. This inhibition of release is reversed by mutations that block binding of the Alix V domain to p6.
The budding and release of nascent virus particles from the infected host cell is an essential phase of the retroviral replication cycle. The budding process requires the trafcking of the Gag polyprotein precursor from its site of synthesis in the cytosol to the appropriate cellular membrane at which virus assembly occurs. Concomitant with particle release from the host cell, the viral protease (PR) cleaves the Gag precursor to generate the mature Gag proteins matrix (MA), capsid (CA) and nucleocapsid (NC). In HIV-1 and equine infectious anemia virus (EIAV), additional domains known as p6 and p9, respectively, are located at the C terminus of the Gag precursor1. p6 and p9, and functionally analogous Gag proteins of other retroviruses, encode the so-called late domains that promote the release of virions from the infected cell24. Late domains function by co-opting the host cells endosomal sorting machinery through direct interactions with dened components of the cellular protein trafcking machinery24.
Three retroviral late domains have been characterized, containing the short sequence motifs P(T/S)AP, PPPY and LYPxnLxxL (where x is any residue and xn is any sequence of n 13 residues), respectively.P(T/S)AP, located in p6, promotes release by interacting with Tsg101, a component of the cellular ESCRT-I protein complex510. The PPPY