Functional consequences of mutational analysis of norovirus protease.

Norovirus protease has been subjected to an extensive mutagenesis study. Ala-scanning mutation at 13 different positions (Trp6, Trp19, Thr27, Leu86, Leu95, Leu97, Met101, Gln117, Leu121, Thr134, Tyr143, Val144, and Val167) led to loss of function and/or stability. Considering the crystal structure of the protease, it was revealed that a hydroxyl group of Thr134 and an aromatic ring of Tyr143 were important for substrate recognition along with His157. It was notable that several of the residues identified were in close proximity to each other, suggesting their importance for the integrity and stability of the protease.