The influence of residue 190 in the S1 site of trypsin-like serine proteases on substrate selectivity is universally conserved.

We examined the influence of Ser/Ala190 in the S1 site on P1 substrate selectivity in several serine proteases. The impact of residue 190 on the selectivity was constant, regardless of differences in original selectivity or reactivity. Substrate binding in S1 was optimised in all wild-type enzymes, while the effects on k(cat) depended on the combination of residue 190 and substrate. Mutagenesis of residue 190 did not affect the S2-S4 sites. Pronounced selectivity for arginine residues was coupled with low enzymatic activity, in particular in recombinant factor IXa. This is due to the dominance of the S1-P1 interaction over substrate binding in the S2-S4 sites.