HPV E6 and MAGUK protein interactions: determination of the molecular basis for specific protein recognition and degradation

It has recently been shown that the high-risk human papillomavirus (HPV) E6 proteins can target the PDZ-domain containing proteins, Dlg, MUPP-1, MAGI- 1 and hScrib for proteasome-mediated degradation. However, the E6 proteins from HPV-16 and HPV-18 (the two most common high-risk virus types) differ i n their ability to target these proteins in a manner that correlates with t heir malignant potential. To investigate the underlying mechanisms for this , we have mutated HPV-16 and HPV-18 E6s to give each protein the other's PD Z-binding motif. Analysis of these mutants shows that the greater ability o f HPV-18 E6 to bind to these proteins and to target them for degradation is indeed due to a single amino acid difference. Using a number of assays, we show that the E6 proteins interact specifically with only one of the five PDZ domains of MAGI-1, and this is the first interaction described for this particular PDZ domain. We also show that the guanylate kinase homology dom ain and the regions of MAGI-1 down stream of amino acid 733 are pot require d for the degradation of MAGI-I. Finally, in a series of comparative analys es, we show that the degradation of MAGI-1 occurs through a different mecha nism from that used by the E6 protein to induce the degradation of DIg and p53.