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Proc Natl Acad Sci U S A. 1988 Nov;85(21):7872-6.

Viral cysteine proteases are homologous to the trypsin-like family of serine proteases: structural and functional implications.

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  • 1Department of Biophysics, University of California, Berkeley 94720.


Proteases that are encoded by animal picornaviruses and plant como- and potyviruses form a related group of cysteine-active-center enzymes that are essential for virus maturation. We show that these proteins are homologous to the family of trypsin-like serine proteases. In our model, the active-site nucleophile of the trypsin catalytic triad, Ser-195, is changed to a Cys residue in these viral proteases. The other two residues of the triad, His-57 and Asp-102, are otherwise absolutely conserved in all the viral protease sequences. Secondary structure analysis of aligned sequences suggests the location of the component strands of the twin beta-barrel trypsin fold in the viral proteases. Unexpectedly, the 2a and 3c subclasses of viral cysteine proteases are, respectively, homologous to the small and large structural subclasses of trypsin-like serine proteases. This classification allows the molecular mapping of residues from viral sequences onto related tertiary structures; we precisely identify amino acids that are strong determinants of specificity for both small and large viral cysteine proteases.

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