3f6u
From Proteopedia
Crystal structure of human Activated Protein C (APC) complexed with PPACK
Structural highlights
DiseasePROC_HUMAN Defects in PROC are the cause of thrombophilia due to protein C deficiency, autosomal dominant (THPH3) [MIM:176860. A hemostatic disorder characterized by impaired regulation of blood coagulation and a tendency to recurrent venous thrombosis. However, many adults with heterozygous disease may be asymptomatic. Individuals with decreased amounts of protein C are classically referred to as having type I protein C deficiency and those with normal amounts of a functionally defective protein as having type II deficiency.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] Defects in PROC are the cause of thrombophilia due to protein C deficiency, autosomal recessive (THPH4) [MIM:612304. A hemostatic disorder characterized by impaired regulation of blood coagulation and a tendency to recurrent venous thrombosis. It results in a thrombotic condition that can manifest as a severe neonatal disorder or as a milder disorder with late-onset thrombophilia. The severe form leads to neonatal death through massive neonatal venous thrombosis. Often associated with ecchymotic skin lesions which can turn necrotic called purpura fulminans, this disorder is very rare. FunctionPROC_HUMAN Protein C is a vitamin K-dependent serine protease that regulates blood coagulation by inactivating factors Va and VIIIa in the presence of calcium ions and phospholipids. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe serine protease domain of activated protein C (APC) contains a Na+ and a Ca2+ site. However, the number and identity of the APC residues that coordinate to Na+ is not precisely known. Further, the functional link between the Na+ and the Ca2+ site is insufficiently defined, and their linkage to the substrate S1 site has not been studied. Here, we systematically investigate the functional significance of these two cation sites and their thermodynamic links to the S1 site. Kinetic data reveal that Na+ binds to the substrate-occupied APC with K(d) values of approximately 24 mm in the absence and approximately 6 mm in the presence of Ca2+. Sodium-occupied APC has approximately 100-fold increased catalytic efficiency ( approximately 4-fold decrease in K(m) and approximately 25-fold increase in k(cat)) in hydrolyzing S-2288 (H-d-Ile-Pro-Arg-p-nitroanilide) and Ca2+ further increases this k(cat) slightly ( approximately 1.2-fold). Ca2+ binds to the protease domain of APC with K(d) values of approximately 438 microm in the absence and approximately 105 microm in the presence of Na+. Ca2+ binding to the protease domain of APC does not affect K(m) but increases the k(cat) approximately 10-fold, and Na+ further increases this k(cat) approximately 3-fold and decreases the K(m) value approximately 3.7-fold. In agreement with the K(m) data, sodium-occupied APC has approximately 4-fold increased affinity in binding to p-aminobenzamidine (S1 probe). Crystallographically, the Ca2+ site in APC is similar to that in trypsin, and the Na+ site is similar to that in factor Xa but not thrombin. Collectively, the Na+ site is thermodynamically linked to the S1 site as well as to the protease domain Ca2+ site, whereas the Ca2+ site is only linked to the Na+ site. The significance of these findings is that under physiologic conditions, most of the APC will exist in Na2+-APC-Ca2+ form, which has 110-fold increased proteolytic activity. Thermodynamic linkage between the S1 site, the Na+ site, and the Ca2+ site in the protease domain of human activated protein C (APC). Sodium ion in the APC crystal structure is coordinated to four carbonyl groups from two separate loops.,Schmidt AE, Padmanabhan K, Underwood MC, Bode W, Mather T, Bajaj SP J Biol Chem. 2002 Aug 9;277(32):28987-95. Epub 2002 May 23. PMID:12029084[15] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
| ||||||||||||||||||||
