The NSP4
protein of rotavirus is a nonstructural
glycoprotein and has a crucial function in virus morphogenesis during
infection of host cells. It was recently reported that NSP4 may also function as a viral
enterotoxin in the induction of rotavirus
diarrhea by causing Ca++ influx in the cytoplasm of the infected cells. We sequenced and analyzed two (Wa and M strains) pairs of NSP4 genes of virulent (v) and attenuated (a) (after 30 to 40 passages in cell culture) human group A rotaviruses and a pair of NSP4 genes of virulent and attenuated porcine group C rotavirus (Cowden strain). These strains were previously identified as virulent (induce
diarrhea) or attenuated (no
diarrhea) in a gnotobiotic pig model of
rotavirus infection [Bohl et al. (4), Saif et
al. (13), Ward et al. (17)]. The NSP4 genes of the Wa, M and Cowden strains were amplified with RT-PCR using a proof reading polymerase (Tli) and the RT-PCR product was sequenced directly. Analysis of the NSP4 deduced amino acid sequences showed that only 3 (Wa) and 2 (M and Cowden)
amino acids differed between the virulent and attenuated strains. For the Wa strain, the changes from the virulent to attenuated strain were in
amino acids 13 (V to A), 16 (L to S) and 34 (P to L); in the M strain, the difference was in
amino acids 53 (T to I) and 104 (K to E), and in the Cowden strains,
amino acids 50 (L to F) and 97 (D to N) differed between virulent and attenuated strains. To our knowledge, this is the first sequence comparison between NSP4 of a virulent and attenuated pair of group C rotaviruses. The potential impact of these few
amino acid changes on the pathogenesis of the NSP4
protein for piglets is unclear, relative to previous findings in mice (1), but requires further study using purified recombinant NSP4
proteins or
peptides.