8os5 | pdb_00008os5
Crystal structure of the Factor XII heavy chain reveals an interlocking dimer with a FnII to kringle domain interaction
Structural highlights
DiseaseFA12_HUMAN Congenital factor XII deficiency;Hereditary angioedema type 3. Defects in F12 are the cause of factor XII deficiency (FA12D) [MIM:234000; also known as Hageman factor deficiency. This trait is an asymptomatic anomaly of in vitro blood coagulation. Its diagnosis is based on finding a low plasma activity of the factor in coagulating assays. It is usually only accidentally discovered through pre-operative blood tests. F12 deficiency is divided into two categories, a cross-reacting material (CRM)-negative group (negative F12 antigen detection) and a CRM-positive group (positive F12 antigen detection).[1] [2] [3] [4] [5] [6] [7] [8] [9] Defects in F12 are the cause of hereditary angioedema type 3 (HAE3) [MIM:610618; also known as estrogen-related HAE or hereditary angioneurotic edema with normal C1 inhibitor concentration and function. HAE is characterized by episodic local subcutaneous edema, and submucosal edema involving the upper respiratory and gastrointestinal tracts. HAE3 occurs exclusively in women and is precipitated or worsened by high estrogen levels (e.g. during pregnancy or treatment with oral contraceptives). It differs from HAE types 1 and 2 in that both concentration and function of C1 inhibitor are normal.[10] [11] FunctionFA12_HUMAN Factor XII is a serum glycoprotein that participates in the initiation of blood coagulation, fibrinolysis, and the generation of bradykinin and angiotensin. Prekallikrein is cleaved by factor XII to form kallikrein, which then cleaves factor XII first to alpha-factor XIIa and then trypsin cleaves it to beta-factor XIIa. Alpha-factor XIIa activates factor XI to factor XIa.[12] Publication Abstract from PubMedThe contact system is composed of Factor XII (FXII), prekallikrein (PK) and co-factor kininogen (HK). The globular C1q receptor (gC1qR) has been shown to interact with FXII and HK. We reveal the FXII fibronectin type II domain (FnII) binds gC1qR in a Zn2+ dependent fashion and determined the complex crystal structure. FXIIFnII binds the gC1qR trimer in an asymmetric fashion with residues Arg36 and Arg65 forming contacts with two distinct negatively charged pockets. gC1qR residues Asp185 and His187 coordinate a Zn2+ adjacent to the FXII binding site and a comparison with the ligand free gC1qR crystal structure reveals the anionic G1-loop becomes ordered upon FXIIFnII binding. Additional conformational changes in the region of the Zn2+ binding site reveal an allosteric basis for Zn2+ modulation of FXII binding. Mutagenesis coupled with SPR demonstrate the gC1qR Zn2+ site contributes to FXII binding and plasma based assays reveal gC1qR stimulates coagulation in a FXII-dependent manner. Analysis of the binding of HK domain 5 (HKD5) to gC1qR shows only one high affinity binding site per trimer. Mutagenesis studies identify a critical G3-loop located at the center of the gC1qR trimer suggesting steric occlusion as the mechanism for HKD5 asymmetric binding. Gel filtration experiments reveal that gC1qR clusters FXII and HK into a higher order 500kDa ternary complex. These results support the conclusion that extracellular gC1qR can act as a chaperone to cluster contact factors which may be a prelude for initiating the cascades which drive bradykinin generation and the intrinsic pathway of coagulation. Factor XII and kininogen asymmetric assembly with gC1qR/C1QBP/P32 is governed by allostery.,Kaira BG, Slater A, McCrae KR, Dreveny I, Sumya UM, Mutch NJ, Searle M, Emsley J Blood. 2020 Jun 19. pii: 461064. doi: 10.1182/blood.2020004818. PMID:32559765[13] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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