Group A Streptococcus
Group A Streptococcus (GAS) infections affect >700M people annually worldwide, with ~18M of these cases severe in nature, and ~600K classified as highly invasive. GAS is a human-specific pathogen responsible for an array of pathological manifestations, ranging from superficial skin and pharynx infections, to severe conditions, e.g., necrotizing fasciitis and toxic shock, and post-infection sequelae that results in rheumatic heart disease and glomerulonephritis. Severe infections have a combined fatality rate of ~30% in western countries. Currently, no GAS vaccine is available and its development has been difficult primarily due to the number of diverse GAS strains and the complications that often arise from cross-reactivity with host proteins. Antibiotics remain effective against GAS infections, however resistant strains have been observed and present a potential threat to public health.
Image 1. Illustration representing the interaction a1a2 region of the plasminogen binding Group A Streptococcal M-like protein (PAM) to the kringle-2 (K2) domain of host plasmin(ogen) (Pg or Pm). The secreted virulence factor streptokinase (SK2b) from PAM-containing GAS strains, like strain AP53, has evolved to preferentially activate host plasminogen bound to PAM. (Characterization of Streptokinases from Group A Streptococci Reveals a Strong Functional Relationship That Supports the Coinheritance of Plasminogen-binding M Protein and Cluster 2b Streptokinase. J. Biol. Chem. 287, 42093–103, 2012).The more virulent strains of GAS subvert host defenses by producing factors that hijack proteins to facilitate dissemination into deep tissue at the expense of altering host vascular integrity. As an example, during infection, GAS is able to exploit components of the host fibrinolytic system, including plasminogen and fibrinogen, promoting systemic infection and permitting the organism to evade an immune response. Early work at the Keck Center has demonstrated that the M-like protein, PAM, found on the bacterial surface of some GAS strains binds to human plasminogen with extremely high affinity. In addition to binding, host plasminogen GAS secretes the potent plasminogen activator streptokinase. The combination of binding and activation of human plasminogen creates a preotolytic microenvironment around the GAS cell surface, allowing the organism to degrade host tissue, dissolve clots, subvert immune response, and colonize host tissue. The importance of human plasminogen to GAS infection has been demonstrated in a number of ways, including the observed increase in virulence in transgenic mice expressing human plasminogen.
The Keck Center uses an interdisciplinary approach focused on identifying mechanisms of host/bacteria interaction and regulatory systems important for GAS virulence. Specifically, detailed structure-function analysis of the binding of GAS surface proteins to host fibrinolytic proteins, plasminogen and fibrinogen, are being performed. In addition, a number of “omics” types of analysis are underway to identify critical genes necessary for GAS host colonization and survival. Animal models of infection are routinely used to probe the role of critical genes and understand aspects of virulence. Together these approaches help to define critical aspects of GAS infection in an effort to prevent and treat the potentially life-threatening diseases it can cause.
Image 1. Illustration representing the interaction a1a2 region of the plasminogen binding Group A Streptococcal M-like protein (PAM) to the kringle-2 (K2) domain of host plasmin(ogen) (Pg or Pm). The secreted virulence factor streptokinase (SK2b) from PAM-containing GAS strains, like strain AP53, has evolved to preferentially activate host plasminogen bound to PAM. (Characterization of Streptokinases from Group A Streptococci Reveals a Strong Functional Relationship That Supports the Coinheritance of Plasminogen-binding M Protein and Cluster 2b Streptokinase. J. Biol. Chem. 287, 42093–103, 2012).
Image 2. NMR structure of a peptide fragment from the a1a2 region of the Group A Streptococcal M-like protein PAM, with residues shown in green, binding to the kringle-2 domain of human plasminogen ,shown in blue. These key interactions allow the human pathogen to recruit plasminogen to the cell surface, a critical aspect of GAS virulence. (Solution structure of the complex of VEK-30 and plasminogen kringle 2. J. Struct. Biol. 169, 349–59, 2010).
Image 3. Streptococcus pyogenes adhering to human keratinocytes. A microscopic image showing a layer of human skin cells that have been infected with S. pyogenes. The small dark chains are representative of GAS adhering to host tissue, at the initiation of the infection.
Glinton K, Beck J, Liang Z, Qiu C, Lee SW, Ploplis VA, Castellino FJ. Variable Region in Streptococcal M-Proteins Provides Stable Binding with Host Fibrinogen for Plasminogen-Mediated Bacterial Invasion. J Biol Chem. 2017 Mar 9. pii: jbc.M116.768937. doi: 10.1074/jbc.M116.768937. [Epub ahead of print] PMID: 28280245
Bao YJ, Shapiro BJ, Lee SW, Ploplis VA, Castellino FJ. Phenotypic differentiation of Streptococcus pyogenes populations is induced by recombination-driven gene-specific sweeps.Sci Rep. 2016 Nov 8;6:36655. Doi: 10.1038/srep36644. PMID: 27821851 [Unknown status]
Bao YJ, Liang Z, Mayfield JA, McShan WM, Lee SW, Ploplis VA, Castellino FJ. Novel genomic rearrangements mediated by multiple genetic elements in Streptococcus pyogenes M23ND confer potential for evolutionary persistence. Microbiology. 2016 Aug; 162(8):1346-59. doi: 10.1099/mic.0.000326 PMID: 27329479 [Unknown status]
Bao YJ, Liang Z, Mayfield JA, Donahue DL, Carothers KE, Lee SW, Ploplis VA, Castellino FJ. Genomic Characterization of a Pattern D Streptococcus pyogenes emm53 Isolate Reveals a Genetic Rationale for Invasive Skin Tropicity. J Bacteriol. 2016 May 27;198(12):1712-24. doi: 10.1128/JB.01019-15. Print 2016 Jun 15. PMID: 27044623 [PubMed - in process]
Agrahari G, Liang Z, Glinton K, Lee SW, Ploplis VA, Castellino FJ. Streptococcus pyogenes Employs Strain-dependent Mechanisms of C3b Inactivation to Inhibit Phagocytosis and Killing of Bacteria. J Biol Chem. 2016 Apr 22;291(17):9181-9. doi: 10.1074/jbc.M115.704221. Epub 2016 Mar 4. PMID: 26945067 [PubMed - in process]
Higashi DL, Biais N, Donahue DL, Mayfield JA, Tessier CR, Rodriguez K, Ashfeld BL, Luchetti J Ploplis VA, Castellino FJ, Lee SW. Activation of band 3 mediates group A Streptococcus streptolysin S-based beta-haemolysis. Nat Microbiol. 2016 Jan 18;1:15004. doi: 10.1038/nmicrobiol.2015.4. PMID: 27571972 [Unknown status]
Chandrahas V, Glinton K, Liang Z, Donahue DL, Ploplis VA, Castellino FJ. Direct Host Plasminogen Binding to Bacterial Surface M-protein in Pattern D Strains of Streptococcus pyogenes is Required for Activation by its Natural Coinherited SK2b. J Biol Chem. 2015 Jun 12. pii: jbc.M115.655365. [Epub ahead of print] PMID: 26070561
Bao Y, Liang Z, Booyjzsen C, Mayfield JA, Lee SW, Ploplis VA, Song H, Castellino FJ. Unique genomic arrangements in an invasive serotype M23 strain of Streptococcus pyogenes identify genes that induce hypervirulence. J Bacteriol.214 Dec; 196(23):4089-102.doi:10.1128/JP.02131-14. Ephub 2014 Sep 15. PMID: 25225265
Mayfield JA, Liang Z, Agrahari G, Lee SW, Donahue DL, Ploplis VA, Castellino FJ. Mutations in the control of virulence sensor gene from Streptococcus pyogenes after infection in mice lead to clonal bacterial variants with altered gene regulatory activity and virulence. PLoS One. 2014 Jun 26;9(6):e100698. doi: 10.1371/journal.pone.0100698. eCollection 2014. PMID:24968349
Bhattacharya S, Liang Z, Quek AJ, Ploplis VA, Law R, Castellino FJ. Dimerization Is Not a Determining Factor for Functional High Affinity Human Plasminogen Binding by the Group A Streptococcal Virulence Factor PAM and Is Mediated by Specific Residues within the PAM a1a2 Domain. J Biol Chem. 2014 Aug 1;289(31):21684-93. doi: 10.1074/jbc.M114.570218. Epub 2014 Jun 24. PMID:24962580
Zhang Y, Mayfield JA, Ploplis VA, Castellino FJ. The β-domain of cluster 2b streptokinase is a major determinant for the regulation of its plasminogen activation activity by cellular plasminogen receptors. Biochem Biophys Res Commun. 2014 Feb 21;444(4):595-8. doi: 10.1016/j.bbrc.2014.01.109. Epub 2014 Jan 31. PMID:24486550
Agrahari G, Liang Z, Mayfield JA, Balsara RD, Ploplis VA, Castellino FJ. Complement-mediated opsonization of invasive group A Streptococcus pyogenes strain AP53 is regulated by the bacterial two-component cluster of virulence responder/sensor (CovRS) system. J Biol Chem. 2013 Sep 20;288(38):27494-504. doi: 10.1074/jbc.M113.494864. Epub 2013 Aug 8. PMID:23928307
Sanderson-Smith ML, Zhang Y, Ly D, Donahue D, Hollands A, Nizet V, Ranson M, Ploplis VA, Walker MJ, Castellino FJ. A key role for the urokinase plasminogen activator (uPA) in invasive Group A streptococcal infection. PLoS Pathog. 2013;9(7):e1003469. doi: 10.1371/journal.ppat.1003469. Epub 2013 Jul 4. PMID:23853591
Zhang Y, Liang Z, Glinton K, Ploplis VA, Castellino FJ. Functional differences between Streptococcus pyogenes cluster 1 and cluster 2b streptokinases are determined by their β-domains. FEBS Lett. 2013 May 2;587(9):1304-9. doi: 10.1016/j.febslet.2013.02.033. Epub 2013 Mar 7. PMID:23474243
Liang Z, Zhang Y, Agrahari G, Chandrahas V, Glinton K, Donahue DL, Balsara RD, Ploplis VA, Castellino FJ. A natural inactivating mutation in the CovS component of the CovRS regulatory operon in a pattern D Streptococcal pyogenes strain influences virulence-associated genes. J Biol Chem. 2013 Mar 1;288(9):6561-73. doi: 10.1074/jbc.M112.442657. Epub 2013 Jan 13. PMID:23316057