Mutation of a conserved residue (D123) required for oligomerization of human immunodeficiency virus type 1 Nef protein abolishes interaction with human thioesterase and results in impairment of Nef biological functions

Nef is a myristoylated protein of 27 to 35 kDa that is conserved in primate lentiviruses. In vivo, Nef is required for high viral load and full pathol ogical effects. In vitro, Nef has at least four activities: induction of CD 4 and major histocompatibility complex (MHC) class I downregulation, enhanc ement of viral infectivity, and alteration of T-cell activation pathways. W e previously reported that the Nef protein from human immunodeficiencj viru s type 1 interacts with a novel human thioesterase (hTE). In the present st udy, by mutational analysis, we identified a region of the Nef core, extend ing from the residues D108 to W124, that is involved both in Nef-hTE intera ction and in Nef-induced CD 1 downregulation. This region of Nef is located on the oligomer interface and is in close proximity to the putative CD4 bi nding site. One of the mutants carrying a mutation in this region, targeted to the conserved residue D123, was also found to be defective in two other functions of Nef, MHC class I downmodulation and enhancement of viral infe ctivity. Furthermore, mutation of this residue affected the ability of Nef to form dimers, suggesting that the oligomerization of Nef may be critical for its multiple functions.