Interscaffolding Additivity. Association of P1 Variants of Eglin c and of Turkey Ovomucoid Third Domain with Serine Proteinases

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• 作者：M. A. Qasim ; Philip J. Ganz ; Charles W. Saunders ; Katherine S. Bateman ; Michael N. G. James ; and Michael Laskowski ; Jr.
• 刊名：Biochemistry
• 出版年：1997
• 出版时间：February 18, 1997
• 年：1997
• 卷：36
• 期：7
• 页码：1598 - 1607
• 全文大小：316K
• 年卷期：v.36,no.7(February 18, 1997)
• ISSN：1520-4995

文摘

Standard mechanism protein inhibitors of serineproteinases share a common mechanism ofinteraction with their cognate enzymes. The P₁ residueof the inhibitor interacts with the enzyme in asubstrate-like manner. Its side chain becomes imbedded in theS₁ cavity of the enzyme. The nature ofP₁, the primary specificity residue, greatly affects thestrength and specificity of the enzyme inhibitorassociation. In canonical inhibitors, residuesP₄-P₂'(P₃'), whereP₁-P₁' is the reactive site, share acommonmain chain conformation that does not change on complex formation.The remainder of the inhibitor'sstructure, the scaffolding, is not always common. Instead, thereare at least 20 inhibitor families, eachwith a different scaffolding. In this paper, we ask whether thedifferences in standard free energy ofassociation of enzyme-inhibitor complexes upon P₁mutations are independent of the nature of thescaffolding. We have already reported on 25 P₁variants of turkey ovomucoid third domain, a memberof the Kazal inhibitor family, interacting with six different serineproteinases. Here, we report on sevendifferent P₁ variants of eglin c, a potato I family member,interacting with the same six serine proteinasesunder the same conditions. The differences in standard free energyon P₁ mutations in the eglin c systemagree very well, when P₁ Pro is omitted. Completeagreement indicates that these P₁ residues areinterscaffolding additive. This is consistent with thesuperimposition of the high-resolution structures ofeglin c and of turkey ovomucoid third domain with chymotrypsin. Inboth cases, the P₁ Leu side chainis similarly oriented in almost indistinguishable specificity pocketsof the enzyme.