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Abstract
Staphylococcus aureus can target a variety of tissues, causing life-threatening infections. The basis for this diversity stems from the microorganism’s ability to spread in the vascular system throughout the body. To survive in blood, S. aureus coats itself with a fibrinogen (Fg)/fibrin shield. The protective shield is assembled by the coordinated actions of a number of Fg-binding bacterial proteins that manipulate the host’s blood coagulation system. Several of the Fg binders appear redundant, sharing similar functional motifs. This observation led us to screen for the presence of novel proteins with significant amino acid identities to von Willebrand factor-binding protein (vWbp), a key component in the shield assembly machinery. One identified protein showed significant sequence identity with the C-terminal region of vWbp, and we consequently named it vWbp homologous protein (vhp). The vhp gene lies within a cluster of genes that encode other virulence factors in S. aureus. Although each isolate only contains one copy of the vhp gene, S. aureus has at least three distinct alleles, vhpA, B, and C, that are present in the core genome. All three vhp isoforms bind Fg with high affinity, targeting a site located in the D fragment of Fg. We further identified an ∼79 amino acid-long, conserved segment within the C-terminal region of vWbp that shares high sequence identities (54 to 67%) with the vhps and binds soluble Fg with high affinity. Further analysis of this conserved motif and the intact vhps revealed intriguing differences in the Fg binding behavior, perhaps suggesting that these proteins have similar but discrete functions in the shield assembly.
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Host fibrinogen drives antimicrobial function in Staphylococcus aureus peritonitis through bacterial-mediated prothrombin activation. Proc Natl Acad Sci U S A 2020; 118:2009837118. [PMID: 33443167 DOI: 10.1073/pnas.2009837118] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The blood-clotting protein fibrinogen has been implicated in host defense following Staphylococcus aureus infection, but precise mechanisms of host protection and pathogen clearance remain undefined. Peritonitis caused by staphylococci species is a complication for patients with cirrhosis, indwelling catheters, or undergoing peritoneal dialysis. Here, we sought to characterize possible mechanisms of fibrin(ogen)-mediated antimicrobial responses. Wild-type (WT) (Fib+) mice rapidly cleared S. aureus following intraperitoneal infection with elimination of ∼99% of an initial inoculum within 15 min. In contrast, fibrinogen-deficient (Fib-) mice failed to clear the microbe. The genotype-dependent disparity in early clearance resulted in a significant difference in host mortality whereby Fib+ mice uniformly survived whereas Fib- mice exhibited high mortality rates within 24 h. Fibrin(ogen)-mediated bacterial clearance was dependent on (pro)thrombin procoagulant function, supporting a suspected role for fibrin polymerization in this mechanism. Unexpectedly, the primary host initiator of coagulation, tissue factor, was found to be dispensable for this antimicrobial activity. Rather, the bacteria-derived prothrombin activator vWbp was identified as the source of the thrombin-generating potential underlying fibrin(ogen)-dependent bacterial clearance. Mice failed to eliminate S. aureus deficient in vWbp, but clearance of these same microbes in WT mice was restored if active thrombin was administered to the peritoneal cavity. These studies establish that the thrombin/fibrinogen axis is fundamental to host antimicrobial defense, offer a possible explanation for the clinical observation that coagulase-negative staphylococci are a highly prominent infectious agent in peritonitis, and suggest caution against anticoagulants in individuals susceptible to peritoneal infections.
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Maddur AA, Kroh HK, Aschenbrenner ME, Gibson BHY, Panizzi P, Sheehan JH, Meiler J, Bock PE, Verhamme IM. Specificity and affinity of the N-terminal residues in staphylocoagulase in binding to prothrombin. J Biol Chem 2020; 295:5614-5625. [PMID: 32156702 PMCID: PMC7186164 DOI: 10.1074/jbc.ra120.012588] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 03/09/2020] [Indexed: 11/06/2022] Open
Abstract
In Staphylococcus aureus-caused endocarditis, the pathogen secretes staphylocoagulase (SC), thereby activating human prothrombin (ProT) and evading immune clearance. A previous structural comparison of the SC(1-325) fragment bound to thrombin and its inactive precursor prethrombin 2 has indicated that SC activates ProT by inserting its N-terminal dipeptide Ile1-Val2 into the ProT Ile16 pocket, forming a salt bridge with ProT's Asp194, thereby stabilizing the active conformation. We hypothesized that these N-terminal SC residues modulate ProT binding and activation. Here, we generated labeled SC(1-246) as a probe for competitively defining the affinities of N-terminal SC(1-246) variants preselected by modeling. Using ProT(R155Q,R271Q,R284Q) (ProTQQQ), a variant refractory to prothrombinase- or thrombin-mediated cleavage, we observed variant affinities between ∼1 and 650 nm and activation potencies ranging from 1.8-fold that of WT SC(1-246) to complete loss of function. Substrate binding to ProTQQQ caused allosteric tightening of the affinity of most SC(1-246) variants, consistent with zymogen activation through occupation of the specificity pocket. Conservative changes at positions 1 and 2 were well-tolerated, with Val1-Val2, Ile1-Ala2, and Leu1-Val2 variants exhibiting ProTQQQ affinity and activation potency comparable with WT SC(1-246). Weaker binding variants typically had reduced activation rates, although at near-saturating ProTQQQ levels, several variants exhibited limiting rates similar to or higher than that of WT SC(1-246). The Ile16 pocket in ProTQQQ appears to favor nonpolar, nonaromatic residues at SC positions 1 and 2. Our results suggest that SC variants other than WT Ile1-Val2-Thr3 might emerge with similar ProT-activating efficiency.
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Affiliation(s)
- Ashoka A Maddur
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-2561.
| | - Heather K Kroh
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-2561
| | - Mary E Aschenbrenner
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-2561
| | - Breanne H Y Gibson
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-2561
| | - Peter Panizzi
- Department of Drug Discovery and Development, Harrison School of Pharmacy, Auburn University, Auburn, Alabama 36849
| | - Jonathan H Sheehan
- Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37232
| | - Jens Meiler
- Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37232; Institute for Drug Discovery, Departments of Chemistry and Computer Science, Leipzig University Medical School, SAC 04103 Leipzig, Germany
| | - Paul E Bock
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-2561
| | - Ingrid M Verhamme
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-2561.
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Thomas S, Liu W, Arora S, Ganesh V, Ko YP, Höök M. The Complex Fibrinogen Interactions of the Staphylococcus aureus Coagulases. Front Cell Infect Microbiol 2019; 9:106. [PMID: 31041195 PMCID: PMC6476931 DOI: 10.3389/fcimb.2019.00106] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2019] [Accepted: 03/27/2019] [Indexed: 11/22/2022] Open
Abstract
The two coagulases, von Willebrand factor binding protein (vWbp) and Coagulase (Coa), are critical virulence factors in several animal models of invasive Staphylococcus aureus (S. aureus) infections. These proteins are part of an intricate system of proteins that S. aureus uses to assemble a fibrinogen (Fg)/fibrin protective shield surrounding itself. This shield allows the microorganism to evade clearance by the host phagocytic cells. The coagulases can non-proteolytically activate the zymogen prothrombin to convert Fg to fibrin and promote the Fg/fibrin shield formation. The coagulases also bind directly to Fg and the interaction between Coa and Fg has been previously characterized in some detail. However, the mechanism(s) by which vWbp interacts with Fg remains unclear. Here, we show that vWbp and Coa have distinct interactions with Fg, despite being structurally similar. Coa binds with a significantly higher affinity to soluble Fg than to Fg coated on a plastic surface, whereas vWbp demonstrates no preference between the two forms of Fg. The two coagulases appear to target different sites on Fg, as they do not compete with each other in binding to Fg. Similar to Coa, both the N- and C-terminal halves of vWbp (vWbp-N, vWbp-C, respectively) harbor Fg-binding activities. The higher affinity Fg-binding activity resides in vWbp-N; whereas, the C-terminal region of Coa encompasses the major Fg-binding activity. Peptides constituting the previously identified Coa/Efb1 Fg-binding motif fail to inhibit vWbp-C from binding to Fg, indicating that vWbp-C lacks a functional homolog to this motif. Interestingly, the N-terminal prothrombin-binding domains of both coagulases recognize the Fg β-chain, but they appear to interact with different sequence motifs in the host protein. Collectively, our data provide insight into the complex interactions between Fg and the S. aureus coagulases.
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Affiliation(s)
- Sheila Thomas
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, TX, United States
| | - Wen Liu
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, TX, United States
| | - Srishtee Arora
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, TX, United States
| | - Vannakambodi Ganesh
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, TX, United States
| | - Ya-Ping Ko
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, TX, United States
| | - Magnus Höök
- Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M University Health Science Center, Houston, TX, United States
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Verhamme IM, Bock PE. Rapid binding of plasminogen to streptokinase in a catalytic complex reveals a three-step mechanism. J Biol Chem 2014; 289:28006-18. [PMID: 25138220 DOI: 10.1074/jbc.m114.589077] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rapid kinetics demonstrate a three-step pathway of streptokinase (SK) binding to plasminogen (Pg), the zymogen of plasmin (Pm). Formation of a fluorescently silent encounter complex is followed by two conformational tightening steps reported by fluorescence quenches. Forward reactions were defined by time courses of biphasic quenching during complex formation between SK or its COOH-terminal Lys(414) deletion mutant (SKΔK414) and active site-labeled [Lys]Pg ([5-(acetamido)fluorescein]-D-Phe-Phe-Arg-[Lys]Pg ([5F]FFR-[Lys]Pg)) and by the SK dependences of the quench rates. Active site-blocked Pm rapidly displaced [5F]FFR-[Lys]Pg from the complex. The encounter and final SK ·[5F]FFR-[Lys]Pg complexes were weakened similarly by SK Lys(414) deletion and blocking of lysine-binding sites (LBSs) on Pg kringles with 6-aminohexanoic acid or benzamidine. Forward and reverse rates for both tightening steps were unaffected by 6-aminohexanoic acid, whereas benzamidine released constraints on the first conformational tightening. This indicated that binding of SK Lys(414) to Pg kringle 4 plays a role in recognition of Pg by SK. The substantially lower affinity of the final SK · Pg complex compared with SK · Pm is characterized by a ∼ 25-fold weaker encounter complex and ∼ 40-fold faster off-rates for the second conformational step. The results suggest that effective Pg encounter requires SK Lys(414) engagement and significant non-LBS interactions with the protease domain, whereas Pm binding additionally requires contributions of other lysines. This difference may be responsible for the lower affinity of the SK · Pg complex and the expression of a weaker "pro"-exosite for binding of a second Pg in the substrate mode compared with SK · Pm.
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Affiliation(s)
- Ingrid M Verhamme
- From the Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
| | - Paul E Bock
- From the Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
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Thomer L, Schneewind O, Missiakas D. Multiple ligands of von Willebrand factor-binding protein (vWbp) promote Staphylococcus aureus clot formation in human plasma. J Biol Chem 2013; 288:28283-92. [PMID: 23960083 DOI: 10.1074/jbc.m113.493122] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Staphylococcus aureus secretes coagulase (Coa) and von Willebrand factor-binding protein (vWbp) to activate host prothrombin and form fibrin cables, thereby promoting the establishment of infectious lesions. The D1-D2 domains of Coa and vWbp associate with, and non-proteolytically activate prothrombin. Moreover, Coa encompasses C-terminal tandem repeats for binding to fibrinogen, whereas vWbp has been reported to associate with von Willebrand factor and fibrinogen. Here we used affinity chromatography with non-catalytic Coa and vWbp to identify the ligands for these virulence factors in human plasma. vWbp bound to prothrombin, fibrinogen, fibronectin, and factor XIII, whereas Coa co-purified with prothrombin and fibrinogen. vWbp association with fibrinogen and factor XIII, but not fibronectin, required prothrombin and triggered the non-proteolytic activation of FXIII in vitro. Staphylococcus aureus coagulation of human plasma was associated with the recruitment of prothrombin, FXIII, and fibronectin as well as the formation of cross-linked fibrin. FXIII activity in staphylococcal clots could be attributed to thrombin-dependent proteolytic activation as well as vWbp-mediated non-proteolytic activation of FXIII zymogen.
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Affiliation(s)
- Lena Thomer
- From the Department of Microbiology, University of Chicago, Chicago, Illinois 60637
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