9pyf
uPA Inhibitory Fab AB2 Complex
Structural highlights
DiseaseUROK_HUMAN Defects in PLAU are the cause of Quebec platelet disorder (QPD) [MIM:601709. QPD is an autosomal dominant bleeding disorder due to a gain-of-function defect in fibrinolysis. Although affected individuals do not exhibit systemic fibrinolysis, they show delayed onset bleeding after challenge, such as surgery. The hallmark of the disorder is markedly increased PLAU levels within platelets, which causes intraplatelet plasmin generation and secondary degradation of alpha-granule proteins.[1] FunctionUROK_HUMAN Specifically cleaves the zymogen plasminogen to form the active enzyme plasmin. Publication Abstract from PubMedAffinity maturation of U33, a recombinant Fab inhibitor of uPA, was used to improve the affinity and the inhibitory effect compared to the parental Fab. Arginine scanning of the six CDR loops of U33 was done to identify initial binding determinants since uPA prefers arginine in its primary substrate binding pocket. Two CDR loops were selected to create an engineered affinity maturation library of U33 that was diversified around ArgL91 (CDR L3) and ArgH52 (CDR H2). Biopanning of the randomized U33 library under stringent conditions resulted in eight Fabs with improved binding properties. One of the most potent inhibitors, AB2, exhibited a 13-fold decrease in IC50 when compared to U33 largely due to a decrease in its off rate. To identify contributions of interfacial residues that might undergo structural rearrangement upon interface formation we used X-ray footprinting and mass spectrometry (XFMS). Four residues showed a pronounced decrease in solvent accessibility, and their clustering suggests that AB2 targets the active site and also engages residues in an adjacent pocket unique to human uPA. The 2.9 A resolution crystal structure of AB2-bound to uPA shows a binding mode in which the CDR L1 loop inserts into the active site cleft and acts as a determinant of inhibition. The selectivity determinant of this binding mode is unlike previously identified inhibitory Fabs against uPA related serine proteases, MTSP-1, HGFA and FXIa. CDRs H2 and L3 loops aid in interface formation and provide critical salt-bridges to remodel loops surrounding the active site of uPA providing specificity and further evidence that antibodies can be potent and selective inhibitors of proteolytic enzymes. Structure of an affinity-matured inhibitory recombinant fab against urokinase plasminogen activator reveals basis of potency and specificity.,Sevillano N, Bohn MF, Zimanyi M, Chen Y, Petzold C, Gupta S, Ralston CY, Craik CS Biochim Biophys Acta Proteins Proteom. 2021 Feb;1869(2):140562. doi: , 10.1016/j.bbapap.2020.140562. Epub 2020 Nov 19. PMID:33221341[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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