title: Effect of reactive site loop elongation on the inhibitory activity of C1-inhibitor.
abstract: The serine protease inhibitor C1-Inhibitor (C1-Inh) inhibits several complement- and contact-system proteases, which play an important role in inflammation. C1-Inh has a short reactive site loop (RSL) compared to other serpins. RSL length determines the inhibitory activity of serpins. We investigated the effect of RSL elongation on inhibitory activity of C1-Inh by insertion of one or two alanine residues in the RSL. One of five mutants had an increased association rate with kallikrein, but was nevertheless a poor inhibitor because of a simultaneous high stoichiometry of inhibition (>10). The association rate of the other variants was lower than that of wild-type C1-Inh. These data suggest that the relatively weak inhibitory activity of C1-Inh is not the result of its short RSL. The short RSL of C1-Inh has, surprisingly, the optimal length for inhibition.
authors.affiliation: Department of Immunopathology, Sanquin Research at CLB, and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Plesmanlaan 125, 1066 CX Amsterdam, The Netherlands. i.bos@sanquin.nl
authors.forename: Ineke G A
authors.initials: IG
authors.lastname: Bos
authors.forename: Yvonne T P
authors.initials: YT
authors.lastname: Lubbers
authors.forename: Eric
authors.initials: E
authors.lastname: Eldering
authors.forename: Jan Pieter
authors.initials: JP
authors.lastname: Abrahams
authors.forename: C Erik
authors.initials: CE
authors.lastname: Hack
mesh_terms: D000409:Alanine / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D003029:Coagulants / Q000037:antagonists & inhibitors; D003174:Complement C1 Inactivator Proteins / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D015956:Factor XIIa / Q000037:antagonists & inhibitors*; D006801:Humans; D007610:Kallikreins / Q000037:antagonists & inhibitors*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010441:Peptide Chain Elongation, Translational; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012697:Serine Endopeptidases / Q000737:chemistry*
chemical_list: D003029:Coagulants; D003174:Complement C1 Inactivator Proteins; D011994:Recombinant Proteins; D007610:Kallikreins; D012697:Serine Endopeptidases; D015956:Factor XIIa; D000409:Alanine