My research is primarily focussed on the serpin superfamily of proteins most of which function as inhibitors of proteolytic enzymes in key physiologic processes such as blood coagulation, fibrinolysis and inflammation. The primary questions being addressed include: 1) what mechanistic features distinguish the serpins from other families of protein inhibitors of proteinases, 2) what governs the specificity of these inhibitors for their cognate proteinases, 3) what is the mechanism of activation of the inhibitors by effectors such as heparin, and 4) what modulating factors act to downregulate or upregulate the inactivation of proteinases by serpin inhibitors so that proteinases accomplish their physiologic function without causing pathologic proteolysis? To address the first three questions, natural and site-directed mutants of serpin inhibitors are being characterized by rapid kinetic and thermodynamic methods to identify the step or steps of proteinase-inhibitor reactions which are defective and thereby to develop a map of the functional sites which mediate the interactions and reactions with proteinases and effectors. Comparisons of serpin inactivation of proteinases in in vitro and in vivo systems are allowing us to address the fourth question. The ultimate goals of my research are to provide not only an understanding of the structure-function relationships in the serpin inhibitors but also to gain insight into the in vivo regulation of proteinases by these inhibitors. Such understanding can serve as the basis for improved treatments of disease states in which the dynamic balance between inhibitor and target proteinase that is essential to proper regulation is disrupted.
Gettins, P. G. W., Patston, P. A., and Olson, S. T. (1996): " Serpins: Structure, function and biology". Austin: R. G. Landes Company. Reviewed in Nature Structural Biology.
Bock, P. E., Day, D. E., Verhamme, I. M. A., Bernardo, M. M., Olson, S. T., and Shore, J. D., "Analogs of Human Plasminogen that Are Labeled with Fluorescence Probes at the Catalytic Site of the Zymogen: Preparation, Characterization, and Interaction with Streptokinase", (1996) J. Biol. Chem. 271, 1072-1080.
Huntington, J. A., Olson, S .T., Fan, B., and Gettins, P .G. W., "Mechanism of Heparin Activation of Antithrombin. Evidence for Reactive Center Loop Pre-insertion with Expulsion upon Heparin Binding", (1996) Biochemistry 35, 8495-8503.
Lawrence, D. A., Palaniappan, S., Stefansson, S., Olson, S. T., Francis-Chmura, A. M., Shore, J. D., and Ginsburg, D., "Characterization of the Binding of Different Conformational Forms of Plasminogen Activator Inhibitor-1 to Vitronectin: Implications for the Regulation of Pericellular Proteolysis", (1997) J. Biol. Chem. 272, 7676-7680.
Rezaie, A. R., and Olson, S. T., "Contribution of Lysine 60f to S1' Specificity of Thrombin", (1996) Biochemistry 36, 1026-1033.
Olson, S. T., Swanson, R., Patston, P. A., and Bjork, I., "Apparent Formation of Sodium Dodecyl Sulfate-Stable Complexes Between Serpins and 3,4-Dichloroisocoumarin-Inactivated Proteinases Is Due to Regeneration of Active Proteinase from the Inactivated Enzyme", (1997) J. Biol. Chem. 272, 13338-13342.
Olson, S. T., Francis-Chmura, A. M., Swanson, R., Bjork, I., and Zettlmeissl, G., "Effect of Individual Carbohydrate Chains of Recombinant Antithrombin on Heparin Affinity and on the Generation of Glycoforms Differing in Heparin Affinity", (1997) Arch. Biochem. Biophys. 341, 212-221.
Turk, B., Brieditis, I., Bock, S. C., Olson, S. T. , and Bjork, I. ,"The Oligosaccharide Side Chain on Asn-135 of a-Antithrombin, Absent in b-Antithrombin, Decreases the Heparin Affinity of the Inhibitor by Affecting the Heparin-Induced Conformational Change", (1997) Biochemistry 36, 6682-6691.
Bock, P. E., Olson, S. T., and Bjork, I., "Inactivation of Thrombin by Antithrombin Is Accompanied by Inactivation of Regulatory Exosite I", (1997) J. Biol. Chem. 272, 19837-19845.
Desai, U. R., Petitou, M., Bjork, I., and Olson, S. T., "Mechanism of Heparin Activation of Antithrombin. Role of Individual Residues of the Pentasaccharide Activating Sequence in the Recognition of Native and Activated States of Antithrombin.", (1998) J. Biol. Chem. 273, 7478-7487.
Bjork, I., Nordling, K., Raub-Segall, E., Hellman, U., and Olson, S. T., "Inactivation of Papain by Antithrombin Due to Autolytic Digestion: A Model of Serpin Inactivation of Cysteine Proteinases", (1998) Biochem. J. 335, 701-709.
Meagher, J. L., Beecham, J. M., Olson, S. T., and Gettins, P. G. W., "Deconvolution of the Fluorescence Emission Spectrum of Human Antithrombin and Identification of the Tryptophan Residues that Are Responsive to Heparin Binding", (1998) J. Biol. Chem. 273, 23283-23289.
Futamura, A., Stratikos, E., Olson, S. T., and Gettins, P. G. W., "Change in Environment of the P1 Side Chain upon Progression from the Michaelis Complex to the Covalent Serpin-Proteinase Complex", (1998) Biochemistry 37, 13110-13119.
Desai, U. R., Petitou, M., Bjork, I., and Olson, S. T., "Mechanism of Heparin Activation of Antithrombin. Evidence for an Induced-Fit Model of Allosteric Activation Involving Two Interaction Subsites", (1998) Biochemistry 37, 13033-13041.
Dharmawardana, K. R., Olson, S. T., and Bock, P. E., "Role of Regulatory Exosite I in Binding of Thrombin to Human Factor V, Factor Va, Factor Va Subunits, and Activation Fragments", (1999) J. Biol. Chem. 274, 18635-18643.
Chuang, Y.-J., Gettins, P. G. W. and Olson, S. T., "Importance of the P2 Glycine of Antithrombin in Target Proteinase Specificity, Heparin Activation, and the Efficiency of Proteinase Trapping as Revealed by a P2 Gly to Pro Mutation", (1999) J. Biol. Chem. 274, 28142-28149.
Arocas, V., Bock, S. C., Olson, S. T., and Bjork, I., "The Role of Arg46 and Arg47 of Antithrombin in Heparin Binding", (1999) Biochemistry 38, 10196-10204.
Meagher, J. L., Olson, S. T., and Gettins, P. G. W., "Critical Role of the Linker Region between Helix D and Strand 2A in Heparin Activation of Antithrombin", (2000) J. Biol. Chem. 275, 2698-2704.
Lawrence, D. A., Olson, S. T., Muhammad, S., Day, D. E., Kvassman, J.-O., Ginsburg, D., and Shore, J. D., "Partitioning of Serpin-Proteinase Reactions between Stable Inhibition and Substrate Cleavage Is Regulated by the Rate of Serpin Reactive Center Loop Insertion into b-Sheet A", (2000) J. Biol. Chem. 275, 5839-5844.
Arocas, V., Turk, B., Bock, S. C., Olson, S. T., and Bjork, I., "The Region of Antithrombin Interacting with Full-Length Heparin Chains Outside the High-Affinity Pentasaccharide Sequence Extends to Lys136 but Not to Lys139", (2000) Biochemistry 39, 8512-8518.
Desai, U., Swanson, R., Bock, S. C., Bjork, I., and Olson, S. T., "Role of Arginine 129 in Heparin Binding and Activation of Antithrombin", (2000) J. Biol. Chem. 275, 18976-18984.
Rezaie, A. R., and Olson, S. T., "Calcium Enhances Heparin Catalysis of the Antithrombin-Factor Xa Reaction by Promoting the Assembly of an Intermediate Heparin-Antithrombin-Factor Xa Bridging Complex. Demonstration by Rapid Kinetic Studies", (2000) Biochemistry 39, 12083-12090.
Estrada, S. Olson, S. T., Raub-Segall, E., and Bjork, I., "The N-terminal Region of Cystatin A (Stefin A) Binds to Papain Subsequent to the Two Hairpin Loops of the Inhibitor. Demonstration of Two-Step Binding by Rapid Kinetic Studies of Cystatin A Labeled at the N-terminus with a Fluorescent Reporter Group", (2000) Protein Science 9, 2218-2224.