Evidence for Activation of Tissue Factor by an Allosteric Disulfide Bond

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• 作者：Vivien M. Chen ; Jasimuddin Ahamed ; Henri H. Versteeg ; Michael C. Berndt ; Wolfram Ruf ; Philip J. Hogg
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：October 3, 2006
• 年：2006
• 卷：45
• 期：39
• 页码：12020 - 12028
• 全文大小：219K
• 年卷期：v.45,no.39(October 3, 2006)
• ISSN：1520-4995

文摘

Tissue Factor (TF) is the mammalian plasma membrane cofactor responsible for initiation ofblood coagulation. Binding of blood coagulation factor VIIa to TF activates the serine proteinase zymogensfactors IX and X by limited proteolysis leading to the formation of a thrombin and fibrin meshwork thatstabilizes the thrombus. TF on the plasma membrane of cells resides mostly in a cryptic configuration,which rapidly transforms into an active configuration in response to certain stimuli. The extracellular partof TF consists of two fibronectin type III domains. The disulfide bond in the membrane proximal domain(Cys186-Cys209) is atypical for domains of this type in that it links adjacent strands in the same images/gifchars/beta2.gif" BORDER=0 ALIGN="middle">sheet, what we have called an allosteric bond. Ablation of the allosteric disulfide by mutating both cysteineresidues severely impairs procoagulant activity. The thiol-alkylating agents N-ethylmaleimide and methylmethanethiolsulfonate block TF activation by ionomycin, while the thiol-oxidizing agent HgCl₂ and dithiolcross-linkers promote activation. TF activation could not be explained by exposure of phosphatidylserineon the outer leaflet of the plasma membrane. Cryptic TF contained unpaired cysteine thiols that weredepleted upon activation, and de-encryption was associated with a change in the conformation of themembrane-proximal domain. These findings imply that the Cys186-Cys209 disulfide bond is reduced inthe cryptic form of TF and that activation involves formation of the disulfide. It is likely that formationof this disulfide bond changes the conformation of the domain that facilitates productive binding of factorsIX and X.