Introduction of α-hydroxymethyamino acid residues in substrate specificity P1 position of trypsin inhibitor SFTI-1 from sunflower seeds retains its activity

In many complexes formed by serine proteinases and their inhibitors, the hydroxyl group provided by water molecule or by the inhibitor Ser residue is located close to the inhibitor P1–P1′ reactive site. In order to investigate the role of this group, we synthesized analogues of trypsin inhibitor SFTI-1 isolated from the seeds of sunflower modified in P1 by α-hydroxymethylserine (HmSer) and both enantiomers of α-hydroxymethylvaline (HmVal). All the synthesized analogues inhibited bovine β-trypsin and human leukocyte elastase. SFTI-1 analogues with HmVal and HmSer appear to be potent inhibitors of bovine β-trypsin, whereas [Val5]SFTI-1 is practically inactive. Also trypsin inhibitory activity of [Ser5]SFTI-1 is significantly lower. Since the electrostatic interaction between protonated ε-NH2 group of the inhibitor P1 position and β-carboxylate of trypsin Asp189 is the main driving force for interaction of both molecules, the results obtained are very interesting. We believe that these SFTI-1 analogues belong to a novel class of serine proteinase inhibitors.