Structural and Biochemical Studies of ALIX/AIP1 and Its Role in Retrovirus Budding

• Published in: Cell 2007-03, Vol.128 (5), p.841-852
• Main Authors: Fisher, Robert D., Chung, Hyo-Young, Zhai, Qianting, Robinson, Howard, Sundquist, Wesley I., Hill, Christopher P.
• Format: Article
• Language: English
• Subjects: Amino Acid Motifs; Calcium-Binding Proteins - chemistry; Calcium-Binding Proteins - metabolism; Carrier Proteins - chemistry; Carrier Proteins - metabolism; Cell Cycle Proteins - chemistry; Cell Cycle Proteins - metabolism; Cell Line; Crystallography, X-Ray; Endosomal Sorting Complexes Required for Transport; Endosomes - metabolism; gag Gene Products, Human Immunodeficiency Virus; Gene Products, gag - metabolism; Glycoproteins - metabolism; HeLa Cells; HIV-1 - chemistry; HIV-1 - drug effects; HIV-1 - growth & development; HIV-1 - metabolism; Humans; Infectious Anemia Virus, Equine - chemistry; Infectious Anemia Virus, Equine - growth & development; Infectious Anemia Virus, Equine - metabolism; Models, Molecular; Mutation; Protein Structure, Tertiary; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - metabolism; Viral Envelope Proteins - metabolism
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/j.cell.2007.01.035

ALIX/AIP1 functions in enveloped virus budding, endosomal protein sorting, and many other cellular processes. Retroviruses, including HIV-1, SIV, and EIAV, bind and recruit ALIX through YPX nL late-domain motifs (X = any residue; n = 1–3). Crystal structures reveal that human ALIX is composed of an N-terminal Bro1 domain and a central domain that is composed of two extended three-helix bundles that form elongated arms that fold back into a “V.” The structures also reveal conformational flexibility in the arms that suggests that the V domain may act as a flexible hinge in response to ligand binding. YPX nL late domains bind in a conserved hydrophobic pocket on the second arm near the apex of the V, whereas CHMP4/ESCRT-III proteins bind a conserved hydrophobic patch on the Bro1 domain, and both interactions are required for virus budding. ALIX therefore serves as a flexible, extended scaffold that connects retroviral Gag proteins to ESCRT-III and other cellular-budding machinery.