Solution structure of anti-HIV-1 and anti-tumor protein MAP30: structural insights into its multiple functions.

We present the solution structure of MAP30, a plant protein with anti-HIV and anti-tumor activities. Structural analysis and subsequent biochemical assays lead to several novel discoveries. First, MAP30 acts like a DNA glycosylase/apurinic (ap) lyase, an additional activity distinct from its known RNA N-glycosidase activity toward the 28S rRNA. Glycosylase/ap lyase activity explains MAP30's apparent inhibition of the HIV-1 integrase, MAP30's ability to irreversibly relax supercoiled DNA, and may be an alternative cytotoxic pathway that contributes to MAP30's anti-HIV/anti-tumor activities. Second, two distinct, but contiguous, subsites are responsible for MAP30's glycosylase/ap lyase activity. Third, Mn2+ and Zn2+ interact with negatively charged surfaces next to the catalytic sites, facilitating DNA substrate binding instead of directly participating in catalysis.