Olga Avrutina, Hans-Ulrich Schmoldt, Dusica Gabrijelcic-Geiger, Dung Le Nguyen, Christian P. Sommerhoff, Ulf Diederichsen, Harald Kolmar
Trypsin inhibition by macrocyclic and open-chain variants of the squash inhibitor MCoTI-II
MCoTI-I and MCoTI-II from the seeds of Momordica cochinchinensis are inhibitors of trypsin-like proteases and the only known members of the large family of squash inhibitors that are cyclic and contain an additional loop connecting the amino- and the carboxy-terminus. To investigate the contribution of macrocycle formation to biological activity, we synthesized a set of open-chain variants of MCoTI-II that lack the cyclization loop and contain various natural and non-natural amino acid substitutions in the reactive-site loop. Upon replacement of P1 lysine residue #10 within the open-chain variant of MCoTI-II by the non-natural isosteric nucleo amino acid AlaG [?-(guanin-9-yl)-L-alanine], a conformationally restricted arginine mimetic, residual inhibitory activity was detected, albeit reduced by four orders of magnitude. While the cyclic inhibitors MCoTI-I and MCoTI-II were found to be very potent trypsin inhibitors, with picomolar inhibition constants, the open-chain variants displayed an approximately 10-fold lower affinity. These data suggest that the formation of a circular backbone in the MCoTI squash inhibitors results in enhanced affinity and therefore is a determinant of biological activity.
Biological Chemistry, Walter de Gruyter
Print ISSN: 1431-6730
Volume: 386, 12/2005
Pages: 1301 - 1306
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