Interaction of peptide boronic acids with elastase: Circular dichroism studies

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Abstract
Boronic acid derivatives of good peptide substrate of the serine proteases cause slow-binding inhibition, manifested as biphasic binding (Kettner and Shenvi: J. Biol. Chem. 259:15106–15114, 1984). These inhibitors are thought to act as reaction-intermediate analogs. Three peptides Boronic acids—Ac-Pro-boro-Val-OH, DNS-Ala-Pro-boro-Val-OH, and Ac-Ala-Ala-Pro-boro-Val-OH—were chosen for farultraviolet circular dichroism (CD) studies in order to determine whether the second phase involves a conformational change of pancreatic elastase. The dipeptide is a simple competitive inhibitors (Ki = 0.27 μM) and the latter are slow-binding inhibitors (Ki = 16.4 and 0.25 nM, respectively). Spectral deconvolution and correction for the formation of antiparallel β-sheet by the peptide inhibitors itself indicate that there is no significant change in the secondary structure of the enzyme in the either the initial or final inhibitors complex. A kinetic experiment confirmed that the slow-binding step was not associated with a CD spectral change, and that therefore a protein conformational change was not responsible for the sow binding.