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Clumping factor A
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Clumping factor A
Clumping factor A is a major virulence factor and a protein from Staphylococcus aureus. It plays a role in several types of infections, such as infective endocarditis, septic arthritis, kidney abscesses, and sepsis/septicemia. ClfA binds to the fibrinogen protein in blood plasma, allowing the bacteria to stick to platelets and begin creating blood clots(thrombus). ClfA binding to fibrinogen is essential in thrombus formation. Fibrinogen is a protein that is made of three pairs of non identical polypeptide chains. It is then broken down by thrombin during blood coagulation, which releases a fibrin monomer. These monomers combine to make a network that gives tensile strength to a blood clot. These fibrin clots are the substrate of the fibrinolytic system.
ClfA also has been shown to bind to complement regulator I protein.
Staphylococcus aureus was first described in 1880 by Sir Alexander Ogston from a surgical abscess in a knee joint.[citation needed] The S. aureus strain Newman is where Clumping factor A was first identified.
ClfA is a surface protein that is anchored to the wall of S. aureus and belongs to the MSCRAMM family, which helps bind bacteria to host extracellular or plasma proteins. Its primary binding partner is the C-terminal region of the γ-chain of fibrinogen. Research shows that the strength of the ClfA–fibrinogen interaction depends heavily on mechanical force. Under low mechanical tension or low shear stress, the interaction is relatively weak, measuring around ~0.1 nN. However, when exposed to high mechanical force, the binding strength increases dramatically to approximately ~1.5 nN. This behavior represents a classic catch-bond mechanism, in which the application of force enhances, rather than disrupts, the stability of a ligand–receptor interaction.
The study further suggests that ClfA contains two distinct binding sites for fibrinogen: a low-affinity site that operates under minimal force and a high-affinity site that becomes engaged when mechanical stress is greater. At a low force, it is suggested that fibrinogen may bind near the top of the N3 domain. While further research needs to be done, these findings indicate that ClfA is mechanically regulated, which allows S. aureus to strengthen adhesion as sheer stress increases, such as during blood flow or when interacting with medical devices like pacemakers and catheters.
ClfA contributes to immune evasion through several complementary mechanisms. By binding fibrinogen and fibrin, ClfA covers bacterial surface antigens that would normally be recognized by immune cells. This “masking” effect prevents efficient opsonization and inhibits phagocyte binding. In addition to steric shielding, ClfA-induced bacterial aggregation forms large clumps that are physically more difficult for neutrophils and macrophages to take over.
ClfA also interacts with complement factor I, which is an enzyme responsible for cleaving C3b into its inactive form, iC3b. When factor I is recruited to the bacterial surface through ClfA, it inactivates complement proteins, reducing opsonization and preventing the assembly of the membrane attack complex.
The ClfA structure contains a ligand-binding region, labeled as the A region, which is composed of three subdomains (N1, N2, N3). The secondary structure contains beta pleated sheets and short alpha helices. The tertiary structure is the three-domain A region (N1, N2, and N3).
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Clumping factor A
Clumping factor A is a major virulence factor and a protein from Staphylococcus aureus. It plays a role in several types of infections, such as infective endocarditis, septic arthritis, kidney abscesses, and sepsis/septicemia. ClfA binds to the fibrinogen protein in blood plasma, allowing the bacteria to stick to platelets and begin creating blood clots(thrombus). ClfA binding to fibrinogen is essential in thrombus formation. Fibrinogen is a protein that is made of three pairs of non identical polypeptide chains. It is then broken down by thrombin during blood coagulation, which releases a fibrin monomer. These monomers combine to make a network that gives tensile strength to a blood clot. These fibrin clots are the substrate of the fibrinolytic system.
ClfA also has been shown to bind to complement regulator I protein.
Staphylococcus aureus was first described in 1880 by Sir Alexander Ogston from a surgical abscess in a knee joint.[citation needed] The S. aureus strain Newman is where Clumping factor A was first identified.
ClfA is a surface protein that is anchored to the wall of S. aureus and belongs to the MSCRAMM family, which helps bind bacteria to host extracellular or plasma proteins. Its primary binding partner is the C-terminal region of the γ-chain of fibrinogen. Research shows that the strength of the ClfA–fibrinogen interaction depends heavily on mechanical force. Under low mechanical tension or low shear stress, the interaction is relatively weak, measuring around ~0.1 nN. However, when exposed to high mechanical force, the binding strength increases dramatically to approximately ~1.5 nN. This behavior represents a classic catch-bond mechanism, in which the application of force enhances, rather than disrupts, the stability of a ligand–receptor interaction.
The study further suggests that ClfA contains two distinct binding sites for fibrinogen: a low-affinity site that operates under minimal force and a high-affinity site that becomes engaged when mechanical stress is greater. At a low force, it is suggested that fibrinogen may bind near the top of the N3 domain. While further research needs to be done, these findings indicate that ClfA is mechanically regulated, which allows S. aureus to strengthen adhesion as sheer stress increases, such as during blood flow or when interacting with medical devices like pacemakers and catheters.
ClfA contributes to immune evasion through several complementary mechanisms. By binding fibrinogen and fibrin, ClfA covers bacterial surface antigens that would normally be recognized by immune cells. This “masking” effect prevents efficient opsonization and inhibits phagocyte binding. In addition to steric shielding, ClfA-induced bacterial aggregation forms large clumps that are physically more difficult for neutrophils and macrophages to take over.
ClfA also interacts with complement factor I, which is an enzyme responsible for cleaving C3b into its inactive form, iC3b. When factor I is recruited to the bacterial surface through ClfA, it inactivates complement proteins, reducing opsonization and preventing the assembly of the membrane attack complex.
The ClfA structure contains a ligand-binding region, labeled as the A region, which is composed of three subdomains (N1, N2, N3). The secondary structure contains beta pleated sheets and short alpha helices. The tertiary structure is the three-domain A region (N1, N2, and N3).