MODIFICATIONS OUTSIDE THE PROTEINASE BINDING LOOP IN CUCURBITA-MAXIMATRYPSIN-INHIBITOR III (CMTI-III) ANALOGS CHANGE THE BINDING-ENERGY WITH BOVINE BETA-TRYPSIN

Five 26-peptide analogues of the trypsin inhibitor [Pro(18)]CMTI-III c ontaining Leu or Tyr in position 7 and Val or Tyr in position 27: 1 (L eu(7), Tyr(27)), 2 (Tyr(7), Val(27)), 3 (Tyr(7) Tyr(27)), 4 (Leu(7), V al(27)) and 5 (Leu(7), Ala(18), Tyr(27)) were synthesized by the solid -phase method. Analogues 1-4 displayed ii, with bovine beta-trypsin of the same order of magnitude as the wild CMTI-III inhibitor, whereas f or analogue 5, this value was lower by about 3 orders of magnitude. Th is indicated that for the analogues with Pro (but not with Ala) in pos ition 18, the sidechain interactions between positions 7 and 27 did no t play a critical role for the stabilization of the active structure. In addition, these results also suggest that Tyr7 is involved in an ad ditional aromatic interaction with position 41 of the enzyme. (C) 1998 Federation of European Biochemical Societies.