4yr6
Fab fragment of 5G6 in complex with epitope peptide
Structural highlights
DiseaseGP1BA_HUMAN Genetic variations in GP1BA may be a cause of susceptibility to non-arteritic anterior ischemic optic neuropathy (NAION) [MIM:258660. NAION is an ocular disease due to ischemic injury to the optic nerve. It usually affects the optic disk and leads to visual loss and optic disk swelling of a pallid nature. Visual loss is usually sudden, or over a few days at most and is usually permanent, with some recovery possibly occurring within the first weeks or months. Patients with small disks having smaller or non-existent cups have an anatomical predisposition for non-arteritic anterior ischemic optic neuropathy. As an ischemic episode evolves, the swelling compromises circulation, with a spiral of ischemia resulting in further neuronal damage.[1] Defects in GP1BA are a cause of Bernard-Soulier syndrome (BSS) [MIM:231200; also known as giant platelet disease (GPD). BSS patients have unusually large platelets and have a clinical bleeding tendency.[2] [3] [4] [5] [6] [7] Defects in GP1BA are the cause of benign mediterranean macrothrombocytopenia (BMM) [MIM:153670; also known as autosomal dominant benign Bernard-Soulier syndrome. BMM is characterized by mild or no clinical symptoms, normal platelet function, and normal megakaryocyte count.[8] Defects in GP1BA are the cause of pseudo-von Willebrand disease (VWDP) [MIM:177820. A bleeding disorder is caused by an increased affinity of GP-Ib for soluble vWF resulting in impaired hemostatic function due to the removal of vWF from the circulation.[9] [10] [11] [12] FunctionGP1BA_HUMAN GP-Ib, a surface membrane protein of platelets, participates in the formation of platelet plugs by binding to the A1 domain of vWF, which is already bound to the subendothelium. Publication Abstract from PubMedEctodomain shedding of glycoprotein (GP) Ibalpha is thought to mediate the clearance of activated, aged or damaged platelets. A monoclonal antibody, 5G6, has been developed recently to specifically bind to the GPIbalpha shedding cleavage site and to inhibit its shedding. However, the molecular mechanism underlying antigen recognition and inhibitory specificity is not clear. To elucidate the structural basis for 5G6 binding to GPIbalpha, we determined the crystal structure of 5G6 Fab fragment in complex with its epitope peptide KL10 (GPIbalpha residues 461-470, KLRGVLQGHL), to 2.4-A resolution. Key residues in both 5G6 and KL10 were mutated to validate their effects in antibody binding by using isothermal titration calorimetry. The 5G6 Fab-KL10 peptide complex structure confirmed the direct association of 5G6 with its target GPIbalpha residues and elucidated the molecular basis underlying its binding specificity and high affinity. The similar binding properties of 5G6 Fab fragment to GPIbalpha on human platelets as those to KL10 suggests that such an interaction may not be affected by the plasma membrane or nearby GPIbbeta. This structural information may facilitate further antibody optimization and humanization. Structural basis for the specific inhibition of glycoprotein Ibalpha shedding by an inhibitory antibody.,Tao Y, Zhang X, Liang X, Zang J, Mo X, Li R Sci Rep. 2016 Apr 22;6:24789. doi: 10.1038/srep24789. PMID:27102061[13] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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