ALIX-CHMP4 interactions in the human ESCRT pathway

Abstract

The ESCRT pathway facilitates membrane fission events during enveloped virus budding, multivesicular body formation, and cytokinesis. To promote HIV budding and cytokinesis, the ALIX protein must bind and recruit CHMP4 subunits of the ESCRT-III complex, which in turn participate in essential membrane remodeling functions. Here, we report that the Bro1 domain of ALIX binds specifically to C-terminal residues of the human CHMP4 proteins (CHMP4A-C). Crystal structures of the complexes reveal that the CHMP4 C-terminal peptides form amphipathic helices that bind across the conserved concave surface of ALIXBro1. ALIX-dependent HIV-1 budding is blocked by mutations in exposed ALIXBro1 residues that help contribute to the binding sites for three essential hydrophobic residues that are displayed on one side of the CHMP4 recognition helix (M/L/IxxLxxW). The homologous CHMP1-3 classes of ESCRT-III proteins also have C-terminal amphipathic helices, but, in those cases, the three hydrophobic residues are arrayed with L/I/MxxxLxxL spacing. Thus, the distinct patterns of hydrophobic residues provide a ''code'' that allows the different ESCRT-III subunits to bind different ESCRT pathway partners, with CHMP1-3 proteins binding MIT domain-containing proteins, such as VPS4 and Vta1/LIP5, and CHMP4 proteins binding Bro1 domaincontaining proteins, such as ALIX.cytokinesis ͉ ESCRT-III ͉ HIV ͉ mutivesicular body

Protein composition of the hepatitis A virus quasi-envelope

“…CHMP4A and CHMP4B (which was identified in the screen; Fig. 2) are known to interact with ALIX and CHMP7 (22,23), and our previous RNAi depletion studies demonstrated that VPS4B is essential for eHAV biogenesis (2). Notably, however, antibody to TSG101, an ESCRT-I-associated protein that unlike ALIX and VPS4B is not required for eHAV biogenesis (2), failed to precipitate eHAV.…”

Mutational Analysis of Candida albicans SNF7 Reveals Genetically Separable Rim101 and ESCRT Functions and Demonstrates Divergence in bro1-Domain Protein Interactions

“…The bro1-domain was first identified in the ESCRT pathway member Bro1 as a Snf7-interaction domain. (Kim et al 2005;McCullough et al 2008). As both Bro1 and Rim20 act as scaffold proteins, Bro1 and Rim20 have been proposed to act as adaptors, promoting downstream Snf7 function toward the ESCRT pathway or the Rim101 pathway, respectively (Boysen and Mitchell 2006).…”

The Roles of ESCRT Proteins in Healthy Cells and in Disease

“…It has not yet been clarified whether this is the case in mammals. The ESCRTs' were found to have a beneficial role in innate immunity by restricting microbial growth and infection (von Schwedler et al, 2003;Vieira et al, 2004;Philips et al, 2008;Morita & Sundquist, 2004;Martin-Serrano & Marsh, 2007;McCullough et al, 2008). The ESCRTs' however, are turned against the host in viral infections.…”

“…Multiple studies have now shown that these host cell pathways can be manipulated by viruses and microorganisms in order to facilitate infection (von Schwedler et al, 2003;Vieira et al, 2004;Philips et al, 2008;Morita & Sundquist, 2004;Martin-Serrano & Marsh, 2007;McCullough et al, 2008). ESCRTs' play an important role in degenerative endosomal trafficking, so it is not surprising that they are involved in killing many microorganisms.…”