title: Engineering an anion-binding cavity in antichymotrypsin modulates the "spring-loaded" serpin-protease interaction.
abstract: Expressed in a kinetically trapped folding state, a serpin couples the thermodynamic driving force of a massive beta-sheet rearrangement to the inhibition of a target protease. Hence, the serpin-protease interaction is the premier example of a "spring-loaded" protein-protein interaction. Amino acid substitutions in the hinge region of a serpin reactive loop can weaken the molecular spring, which converts the serpin from an inhibitor into a substrate. To probe the molecular basis of this conversion, we report the crystal structure of A349R antichymotrypsin in the reactive loop cleaved state at 2.1 A resolution. This amino acid substitution does not block the beta-sheet rearrangement despite the burial of R349 in the hydrophobic core of the cleaved serpin along with a salt-linked acetate ion. The inhibitory activity of this serpin variant is not obliterated; remarkably, its inhibitory properties are anion-dependent due to the creation of an anion-binding cavity in the cleaved serpin.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia 19104, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Lukacs
authors.forename: H
authors.initials: H
authors.lastname: Rubin
authors.forename: D W
authors.initials: DW
authors.lastname: Christianson
mesh_terms: D000838:Anions; D001483:Base Sequence; D001665:Binding Sites; D002918:Chymotrypsin / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics; D018360:Crystallography, X-Ray; D017931:DNA Primers / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D015202:Protein Engineering; D017510:Protein Folding; D017433:Protein Structure, Secondary; D015843:Serpins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D000838:Anions; D017931:DNA Primers; D015843:Serpins; D002918:Chymotrypsin