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Staphylocoagulase is a prototype for the mechanism of cofactor-induced zymogen activation


Many bacterial pathogens secrete proteins that activate host trypsinogen-like enzyme precursors, most notably the proenzymes of the blood coagulation and fibrinolysis systems1,2. Staphylococcus aureus, an important human pathogen implicated in sepsis and endocarditis3, secretes the cofactor staphylocoagulase, which activates prothrombin, without the usual proteolytic cleavages, to directly initiate blood clotting4,5. Here we present the 2.2 Å crystal structures of human α-thrombin and prethrombin-2 bound to a fully active staphylocoagulase variant. The cofactor consists of two domains, each with three-helix bundles; this is a novel fold that is distinct from known serine proteinase activators, particularly the streptococcal plasminogen activator streptokinase6. The staphylocoagulase fold is conserved in other bacterial plasma-protein-binding factors and extracellular-matrix-binding factors7,8,9. Kinetic studies confirm the importance of isoleucine 1 and valine 2 at the amino terminus of staphylocoagulase for zymogen activation. In addition to making contacts with the 148 loop and (pro)exosite I of prethrombin-2, staphylocoagulase inserts its N-terminal peptide into the activation pocket of bound prethrombin-2, allosterically inducing functional catalytic machinery. These investigations demonstrate unambiguously the validity of the zymogen-activation mechanism known as ‘molecular sexuality’10.

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Figure 1: Domain organization of human prothrombin and ZAAPs.
Figure 2: Structure of the human α-thrombin•Met-SC(1–325) complex.
Figure 3: Thrombin–staphylocoagulase interface.
Figure 4: Contribution of the staphylocoagulase N-terminal peptide to zymogen activation.


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We are grateful to Diagnostica Stago for the S. aureus strain, to R. Mentele for sequencing, to G. Bourenkov for help during data collection, and to S. Iwanaga for initiating the project. We thank E. Consacro, H. Kroh and S. Stuart for excellent technical assistance. This work was supported by a National Institutes of Health (NIH) grant to P.E.B., as well as funding from SFB469, the EU project SPINE and the Fonds der Chemischen Industrie. P.P. and P.J.A were supported in part by NIH training grants.

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Correspondence to Wolfram Bode or Paul E. Bock.

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Supplementary information


Supplementary Figure: The sequence of the crystallized SC (S. aureus Newman 2D, strain Tager 104) is compared with two other SCs and several homologs. Strictly conserved residues and conservative substitutions throughout are highlighted in red and pink, respectively; and additional conserved residues are highlighted in yellow. SC residues that contact the 148-loop or exosite I are indicated with closed or open triangles, respectively. The conserved RGD motif in SfbX is shadowed blue. (JPG 281 kb)


Supplementary Figure: Stereo ribbon plot showing the symmetric dimer present in the asymmetric unit, with thrombin and SC moieties colored yellow and orange, and red and salmon, respectively. The terminal SC residues as well as single helices are labeled. (JPG 150 kb)


Supplementary Figure: A superimposition of the µ-plasmin·SK (yellow) and Pre-2·SC(325) (red) complexes. Note the different arrangement around the respective proteinase. (PPT 549 kb)

Supplementary Movie: Zoom from standard orientation into the activation pocket of Pre-2. SC is coloured yellow, the surface of Pre-2 according to the surface potential (blue: positive, red: negative). (MOV 982 kb)

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Friedrich, R., Panizzi, P., Fuentes-Prior, P. et al. Staphylocoagulase is a prototype for the mechanism of cofactor-induced zymogen activation. Nature 425, 535–539 (2003).

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