cis-inhibition of proteasomal degradation by viral repeats: impact of length and amino acid composition

The Gly-Ala repeat (GAr) of the Epstein-Barr virus nuclear antigen 1 is a c is acting inhibitor of ubiquitin-proteasome proteolysis. We have investigat ed the capacity of various repeats to inhibit the turnover of the proteasom al substrate I kappaB alpha. Inhibition of TNF alpha -induced degradation w as achieved by insertion of octamers containing three alanines or valines, interspersed by no more then three consecutive glycines, The inhibitory act ivity was abolished by increasing the length of the spacer, by eliminating the spacers, or by substitution of a single hydrophobic residue with a pola r or charged residue. A serine containing octamer was inactive but inhibiti on was partially restored by insertion of three consecutive repeats. These findings suggest a model where inhibition requires the interaction of at le ast three alanine residues of the GAr in a beta -strand conformation with a djacent hydrophobic binding pockets of a putative receptor. (C) 2001 Federa tion of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.