title: Expression and characterization of recombinant Manduca sexta serpin-1B and site-directed mutants that change its inhibitory selectivity.
abstract: Hemolymph of Manduca sexta contains a number of serine proteinase inhibitors from the serpin superfamily. During formation of a stable complex between a serpin and a serine proteinase, the enzyme cleaves a specific peptide bond in an exposed loop (the reactive-site region) at the surface of the serpin. The amino acid residue on the amino-terminal side of this scissile bond, the P1 residue, is important in defining the selectivity of a serpin for inhibiting different types of serine proteinases. M. sexta serpin-1B, with alanine at the position predicted from sequence alignments to be the P1 residue, was previously named alaserpin. This alanyl residue was changed by site-directed mutagenesis to lysine (A343K) and phenylalanine (A343F). The serpin-1B cDNA and its mutants were inserted into an expression vector, H6pQE-60, and the serpin proteins were expressed in Escherichia coli. Affinity-purified recombinant serpins selectively inhibited mammalian serine proteinases: serpin-1B inhibited elastase; serpin-1B(A343K) inhibited trypsin, plasmin, and thrombin; serpin-1B(A343F) inhibited chymotrypsin as well as trypsin. All three serpins inhibited human cathepsin G. This insect serpin and its site-directed mutants associated with mammalian serine proteinases at rates similar to those reported for mammalian serpins. Serpin-1B and its mutants formed SDS-stable complexes with the enzymes they inhibited. The scissile bond was determined to be between residues 343 and 344 in wild-type serpin-1B and in serpin-1B with mutations at residue 343. These results demonstrate that the P1 alanine residue defines the primary selectivity of serpin-1B for elastase-like enzymes, and that this selectivity can be altered by mutations at this position.
authors.affiliation: Department of Biochemistry, Kansas State University, Manhattan 66506, USA.
authors.forename: H
authors.initials: H
authors.lastname: Jiang
authors.forename: A B
authors.initials: AB
authors.lastname: Mulnix
authors.forename: M R
authors.initials: MR
authors.lastname: Kanost
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D017344:Genes, Insect; D018402:Manduca / Q000201:enzymology / Q000235:genetics*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011993:Recombinant Fusion Proteins / Q000235:genetics; D015842:Serine Proteinase Inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015843:Serpins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D017931:DNA Primers; D011993:Recombinant Fusion Proteins; D015842:Serine Proteinase Inhibitors; D015843:Serpins