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== Publication Abstract from PubMed ==
== Publication Abstract from PubMed ==
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The zymogen prothrombin is proteolytically converted by factor Xa to the active protease thrombin in a reaction that is accelerated &gt;3,000-fold by cofactor Va. This physiologically important effect is paradigmatic of analogous cofactor-dependent reactions in the coagulation and complement cascades, but its structural determinants remain poorly understood. Prothrombin has three linkers connecting the N-terminal Gla domain to kringle-1 (Lnk1), the two kringles (Lnk2), and kringle-2 to the C-terminal protease domain (Lnk3). Recent developments indicate that the linkers, and particularly Lnk2, confer on the zymogen significant flexibility in solution and enable prothrombin to sample alternative conformations. The role of this flexibility in the context of prothrombin activation was tested with several deletions. Removal of Lnk2 in almost its entirety (ProTDelta146-167) drastically reduces the enhancement of thrombin generation by cofactor Va from &gt;3,000-fold to 60-fold because of a significant increase in the rate of activation in the absence of cofactor. Deletion of Lnk2 mimics the action of cofactor Va and offers insights into how prothrombin is activated at the molecular level. The crystal structure of ProTDelta146-167 reveals a contorted architecture where the domains are not vertically stacked, kringle-1 comes within 9 A of the protease domain, and the Gla-domain primed for membrane binding comes in contact with kringle-2. These findings broaden our molecular understanding of a key reaction of the blood coagulation cascade where cofactor Va enhances activation of prothrombin by factor Xa by compressing Lnk2 and morphing prothrombin into a conformation similar to the structure of ProTDelta146-167.
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A flexible linker (Lnk2) composed of 26 amino acids connects kringle-1 to kringle-2 in the coagulation factor prothrombin. Recent studies point to Lnk2 as a key determinant of the structure and function of this zymogen. Using a combination of mutagenesis, structural biology and single molecule spectroscopy we show how Lnk2 influences activation and conformational plasticity of prothrombin. Scrambling the sequence of Lnk2 is inconsequential on activation, and so is extension by as many as 22 residues. On the other hand, below a critical length of 15 residues, the rate of prothrombin activation increases (10-fold) in the absence of cofactor Va, and decreases (3-fold) in the presence of cofactor. Furthermore, activation by prothrombinase takes place without preference along the prethrombin-2 (cleavage at R271 first) or meizothrombin (cleavage at R320 first) pathways. Notably, these transitions in the rate and pathway of activation require the presence of phospholipids, pointing to an important physiological role for Lnk2 when prothrombin is anchored to the membrane. Two new crystal structures of prothrombin lacking 22 (ProTDelta146-167) or 14 (ProTDelta154-167) residues of Lnk2 document striking conformational rearrangements of domains located across this linker. FRET measurements of freely diffusing single molecules prove that these structural transitions are genuine properties of the zymogen in solution. These findings support a molecular model of prothrombin activation where Lnk2 presents the sites of cleavage at R271 and R320 to factor Xa in different orientations by pivoting the C-terminal kringle-2/protease domain pair on the N-terminal Gla domain/kringle-1 pair anchored to the membrane.
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The linker connecting the two kringles plays a key role in prothrombin activation.,Pozzi N, Chen Z, Pelc LA, Shropshire DB, Di Cera E Proc Natl Acad Sci U S A. 2014 May 27;111(21):7630-5. doi:, 10.1073/pnas.1403779111. Epub 2014 May 12. PMID:24821807<ref>PMID:24821807</ref>
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How the Linker Connecting the Two Kringles Influences Activation and Conformational Plasticity of Prothrombin.,Pozzi N, Chen Z, Di Cera E J Biol Chem. 2016 Jan 12. pii: jbc.M115.700401. PMID:26763231<ref>PMID:26763231</ref>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>

Revision as of 18:23, 27 January 2016

Crystal structure of prothrombin deletion mutant residues 146-167 ( Form II ).

5edk, resolution 3.21Å

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