The Nef protein of human immunodeficiency virus
type I (HIV-1) is an important determinant for the onset
of AIDS disease. The self-association properties of HIV-1
Nef are analyzed by chemical cross-linking, dynamic light
scattering, equilibrium analytical ultracentrifugation,
and NMR spectroscopy. The experimental data show that the
HIV-1 Nef core domain forms stable homo-dimers and trimers
in solution, but not higher oligomers. These Nef homomers
are not covalently linked by disulfide bridges, and the
equilibrium between these forms is dependent on the Nef
concentration. We further provide the molecular basis for
the Nef core dimers and trimers obtained by analysis of
crystallographic models. Oligomerization of biological
polypeptides is a common tool used to trigger events in
cellular signaling and endocytosis, both of which are targeted
by Nef. The quaternary structure of Nef may be of physiological
importance and may help to connect its cellular targets
or to increase affinity of the viral molecule for its ligands.
The herein described models for Nef dimers and trimers
will allow further mutational studies to elucidate their
role in vivo. These results provide novel insight into
the structural and functional relationships of this important
viral protein. Moreover, the oligomer interface may represent
a novel target for the design of antiviral agents.