The transition of bovine trypsinogen to a trypsin-like state upon strong ligand binding. II. The binding of the pancreatic trypsin inhibitor and of isoleucine-valine and of sequentially related peptides to trypsinogen and to p-guanidinobenzoate-trypsinogen

Bode, W.

Journal of Molecular Biology 127(4): 357-374

1979


ISSN/ISBN: 0022-2836
PMID: 311834
DOI: 10.1016/0022-2836(79)90227-4
Accession: 017493184

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Abstract
p-Guanidinobenzoate-trypsinogen is transformed into a trypsin-like conformation upon binding of Ile-Val as evidenced by specific changes in its circular dichroism spectrum. By means of this signal the association constants for the binding of a variety of peptides sequentially analogous to either the bovine trypsin N-terminus or to the N-terminal activation peptide sequences of several trypsinogens have been determined at different Ca2+ concentrations. Ile-Val and Ile-Val-Gly exhibit the strongest binding affinity of all peptides investigated. Replacement of the first isoleucine or of the second valine residue by other amino acids considerably reduces the peptide affinity. Discussion of these is based on the known spatial arrangement of the Ile16-Val17-Gly18 N-terminus and of the Ile-Val dipeptide in the Ile16 cleft (crystal structures of bovine trypsin and of the trypsinogen-PTI‡-Ile-Val complex; Bode et al., 1978). The free energies of binding of the first and of the second peptide residue are almost additive indicating independency between both subsites. The third residue, glycine, does not significantly contribute to binding. The peptide analogues of various trypsinogen N-termini exhibit no measurable affinity for the Ile 16 cleft.