Crystal structure of the oligomerization domain of NSP4 from rotavirus reveals a core metal-binding site

During the maturation of rotaviral particles, non-structural protein 4 (NSP 4) plays a critical role in the translocation of the immature capsid into t he lumen of the endoplasmic reticulum. Full-length NSP4 and a 22 amino acid peptide (NSP4(114-135)) derived from this protein have been shown to induc e diarrhea in young mice in an age-dependent manner, and may therefore be t he agent responsible for rotavirally-induced symptoms. We have determined t he crystal structure of the oligomerization domain of NSP4 which spans resi dues 95 to 137 (NSP4(95-137)). NSP4(95-137) self-associates into a parallel , tetrameric coiled-coil, with the hydrophobic core interrupted by three po lar layers occupying a and d-heptad pos -itions. Side-chains from two conse cutive polar layers, consisting of four Gln123 and two of the four Glu120 r esidues, coordinate a divalent cation. Two independent structures built fro m MAD-phased data indicated the presence of a strontium and calcium ion bou nd at this site, respectively. This metal-binding site appears to play an i mportant role in stabilizing the homo-tetramer, which has implications for the engagement of NSP4 as an enterotoxin. (C) 2000 Academic Press.