Binding of native and [homoserine lactone-52]-52,53-seco-bovine basic pancreatic trypsin inhibitor (kunitz inhibitor) to porcine pancreatic β-kallikrein-B and bovine α-chymtorpsin: Thermodynaic study
✍ Scribed by Rolando Oddone; Donatella Barra; Gino Amiconi; Paolo Ascenzi; Cataldo Tarricone; Martino Bolognesi; Fabrizio Bortolotti; Enea Menegatti
- Publisher
- John Wiley and Sons
- Year
- 1994
- Tongue
- English
- Weight
- 901 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0952-3499
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✦ Synopsis
Abstract
Values of the association equilibrium constant (K~a~) for the binding of the native and of the cyanogen bromide‐cleaved bovine basic pancreatic trypsin inhibitor (native BPTI and [Hse lactone‐52]‐52,53‐seco‐BPTI, respectively) to neuraminidase‐treated porcine pancreatic β‐Kallikrein‐B (kallikrein) and bovine α‐chymotrypsin (chymotrypsin) have been determined between pH4.0 and 9.0, and 20.0°C. Over the whole pH range explored, native BPTI and [Hse lactone‐52]‐52,53‐seco‐BPTI show the same affinity for kallikrein. On the other hand, the affinity of [se lactone‐52]‐52,53‐seco‐BPTI for chymotrypsin is high4er, around neutrality, than that found for native BPTI by about one order of magnitude, coverging in the acidic pH limb. The simplest mechanism accounting for the observed data implies that, on lowering the pH from 9.0 to 4.0 (i) the decrease in affinity for the binding of native BPTI to kalikrein and chymotrypsin, as well as for the association of [Hse lactone‐52]‐52,53‐seco‐BPTI to kalikrein, reflects the acidic p__K__ shift, upon inhibitor association, of a single inozing group; and (ii) the decrease of K~a~ values for [Hse lactone‐52]‐52,53‐seco‐BPTI binding to chymotrypsin appears to be modulated by the acidic p__K__ shift, upon inhibitor association, of two non‐equivalent proton‐binding residues. On the basis of the stereochemistry of the serine proteinase/inhibitor contact region(s), these data indicate that long‐rang structural changes in [Hse lactone‐52]‐52,53‐seco‐BPTI are energetically linked to the chymotrypsin: inhibitor complex formation. This observation represents an important aspect for the mechanism of molecular recognition and regulation in BPTI.