Abstract Number: OC 37.2
Meeting: ISTH 2021 Congress
Background: The αIIbβ3 integrin receptor coordinates platelet adhesion, activation, and mechano-sensing in thrombosis and haemostasis. We have identified a disulfide bond in the αIIb subunit thigh domain linking cysteines 490 and 545 that is not formed in about 1 in 3 integrin molecules on the resting and activated human platelet surface. This alternate covalent form of αIIbβ3 is pre-determined as it is also produced by megakaryoblasts and transfected bovine hamster kidney cells.
Aims: To determine the platelet distribution and function of this alternate covalent form of αIIbβ3 integrin.
Methods: Distribution of the alternate αIIbβ3 form on the platelet surface was measured by co-immunoprecipitation experiments and differential cysteine alkylation and mass spectrometry. Conformation of the alternate form was assessed using monoclonal antibodies and molecular dynamic simulations. The function of the C490-C545 disulfide bond was evaluated in BHK cells expressing a mutant αIIbβ3 integrin with an ablated bond.
Results: The alternate covalent form of αIIbβ3 selectively partitions into focal adhesions on the activated platelet surface. The disulfide mutant integrin in BHK cells has extended residency time in focal adhesions due to reduced rate of clathrin-mediated integrin internalisation and recycling, which is associated with enhanced affinity of the αIIb subunit for clathrin adaptor protein-2. Fibrinogen binding and outside-in signalling of the disulfide mutant integrin is reduced due to restrictions on integrin extension measured using monoclonal antibodies, which is supported by molecular dynamic simulations of unbending at the αIIb subunit knee joint.
Conclusions: Megakaryocytes produce an αIIbβ3 integrin containing an unpaired C490-C545 disulfide bond that is selectively sorted into focal adhesions on the platelet surface where it has extended residency time and altered function. These findings indicate that αIIbβ3 integrin receptor is produced in different covalent forms that have different functions. This discovery has implications for platelet function in thrombosis and anti-integrin drug development.
To cite this abstract in AMA style:Pijning AE, Blyth MT, Coote M, Passam F, Chiu J, Hogg PJ. Identification of an Alternate Covalent Form of Platelet αIIbβ3 Integrin that Selectively Partitions into Focal Adhesions where it Has Extended Residency Time and Altered Function [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 1). https://abstracts.isth.org/abstract/identification-of-an-alternate-covalent-form-of-platelet-%ce%b1iib%ce%b23-integrin-that-selectively-partitions-into-focal-adhesions-where-it-has-extended-residency-time-and-altered-function/. Accessed September 16, 2021.
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