Anti-HIV and anti-tumor protein MAP30, a 30 kDa single-strand type-I RIP, shares similar secondary structure and beta-sheet topology with the A chainof ricin, a type-II RIP

MAP30 is a 30 kDa single-stranded, type-I ribosome inactivating protein (RI P) possessing anti-tumor and anti-HIV activities. It binds both ribusomal R NA and the HIV-I long-terminal repeat DNA. To understand the structural bas is for MAP30 activities, we undertook the study of MAP30 by solution NMR sp ectroscopy. We report nearly complete H-1, C-13, and N-15 chemical shift as signments of its 263 amino acids. Based upon an analysis of secondary C-13 chemical shifts, (3)J(HNHA) coupling constants, hydrogen exchange data, and nuclear Overhauser effect patterns, we find that the secondary structure a nd P-sheet topology of MAP30 are very similar to those of the ricin A chain , a subunit of the well-known type-II RIP, even though two proteins display distinct activities. we therefore suggest that MAP30 and ricin A chain sha re a similar three-dimensional fold, and that the reported functional diffe rences between two proteins arise primarily from differences in local three -dimensional structure and other structural properties such as surface elec trostatic potentials.