5hgg
From Proteopedia
Crystal structure of uPA in complex with a camelid-derived antibody fragment
Structural highlights
Disease[UROK_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] Function[UROK_HUMAN] Specifically cleaves the zymogen plasminogen to form the active enzyme plasmin. Publication Abstract from PubMedA peptide segment that binds the active site of a serine protease in a substrate-like manner may behave like an inhibitor or a substrate. However, there is sparse information on which factors determine which behavior a particular peptide segment will exhibit. Here, we describe the first X-ray crystal structure of a nanobody in complex with a serine protease. The nanobody displays a new type of interaction between an antibody and a serine protease as it inserts its CDR-H3 loop into the active site of the protease in a substrate-like manner. The unique binding mechanism causes the nanobody to behave as a strong inhibitor as well as a poor substrate. Intriguingly, its substrate behavior is incomplete, as 30-40% of the nanobody remained intact and inhibitory after prolonged incubation with uPA. Biochemical analysis reveals that an intra-loop interaction network within the CDR-H3 of the nanobody balances its inhibitor versus substrate behavior. Collectively, our results unveil molecular factors, which may be a general mechanism to determine the substrate versus inhibitor behavior of other protease inhibitors. A Camelid-derived Antibody Fragment Targeting the Active Site of a Serine Protease Balances between Inhibitor and Substrate Behavior.,Kromann-Hansen T, Oldenburg E, Yung KW, Ghassabeh GH, Muyldermans S, Declerck PJ, Huang M, Andreasen PA, Ngo JC J Biol Chem. 2016 May 23. pii: jbc.M116.732503. PMID:27226628[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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