The human pathogenic bacterium group A Streptococcus produces an extracellular cysteine protease [streptococcal pyrogenic exotoxin B (SpeB)] that is a critical virulence factor for invasive disease episodes. Sequence analysis of the speB gene from 200 group A Streptococcus isolates collected worldwide identified three main mature SpeB (mSpeB) variants. One of these variants (mSpeB2) contains an Arg-Gly-Asp (RGD) sequence, a tripeptide motif that is commonly recognized by integrin receptors. mSpeB2 is made by all isolates of the unusually virulent serotype M1 and several other geographically widespread clones that frequently cause invasive infections. Only the mSpeB2 variant bound to transfected cells expressing integrin ␣ v ␤ 3 (also known as the vitronectin receptor) or ␣ IIb ␤ 3 (platelet glycoprotein IIb-IIIa), and binding was blocked by a mAb that recognizes the streptococcal protease RGD motif region. In addition, mSpeB2 bound purified platelet integrin ␣ IIb ␤ 3 . Defined ␤ 3 mutants that are altered for fibrinogen binding were defective for SpeB binding. Synthetic peptides with the mSpeB2 RGD motif, but not the RSD sequence present in other mSpeB variants, blocked binding of mSpeB2 to transfected cells expressing ␣ v ␤ 3 and caused detachment of cultured human umbilical vein endothelial cells. The results (i) identify a Gram-positive virulence factor that directly binds integrins, (ii) identify naturally occurring variants of a documented Gram-positive virulence factor with biomedically relevant differences in their interactions with host cells, and (iii) add to the theme that subtle natural variation in microbial virulence factor structure alters the character of hostpathogen interactions.Group A Streptococcus (GAS) is a human pathogenic bacterium that causes diverse infections ranging in severity from relatively mild pharyngitis to life-threatening toxic shock syndrome and necrotizing fasciitis (1). GAS is composed of a heterogeneous array of chromosomal genotypes, and substantial levels of allelic variation also exist in genes encoding putative and proven virulence factors that mediate hostpathogen interactions (2-5). With the exception of M protein, whose structural variation helps GAS evade the type-specific immune response of the host (6), there has been little investigation of the potential ramifications of GAS allelic variation for host-pathogen interactions.GAS isolates produce a highly conserved extracellular cysteine protease known as streptococcal pyrogenic exotoxin B (SpeB) (reviewed in ref. 5). SpeB is initially expressed as a 40-kDa zymogen but then is converted to a 28-kDa active protease by proteolytic truncation (5, 7). SpeB is a critical virulence factor in two mouse models of invasive disease (8, 38) and human infections (5). Purified SpeB causes a cytopathic effect on cultured human endothelial cells (3) and has been shown to activate a host matrix metalloprotease (9).Integrins are heterodimeric membrane proteins located on the surface of mammalian cells that participate in ce...

Streptococcal inhibitor of complement (Sic) is a secreted protein made predominantly by serotype M1 Group A Streptococcus (GAS), which contributes to persistence in the mammalian upper respiratory tract and epidemics of human disease. Unexpectedly, an isogenic sic-negative mutant adhered to human epithelial cells significantly better than the wild-type parental strain. Purified Sic inhibited the adherence of a sic negative serotype M1 mutant and of non-Sic-producing GAS strains to human epithelial cells. Sic was rapidly internalized by human epithelial cells, inducing cell flattening and loss of microvilli. Ezrin and moesin, human proteins that functionally link the cytoskeleton to the plasma membrane, were identified as Sic-binding proteins by affinity chromatography and matrix-assisted laser desorption͞ionization time-of-flight mass spectrometry analysis. Sic colocalized with ezrin inside epithelial cells and bound to the F-actin-binding site region located in the carboxyl terminus of ezrin and moesin. Synthetic peptides corresponding to two regions of Sic had GAS adherence-inhibitory activity equivalent to mature Sic and inhibited binding of Sic to ezrin. In addition, the sic mutant was phagocytosed and killed by human polymorphonuclear leukocytes significantly better than the wild-type strain, and Sic colocalized with ezrin in discrete regions of polymorphonuclear leukocytes. The data suggest that binding of Sic to ezrin alters cellular processes critical for efficient GAS contact, internalization, and killing. Sic enhances bacterial survival by enabling the pathogen to avoid the intracellular environment. This process contributes to the abundance of M1 GAS in human infections and their ability to cause epidemics. microbiology ͉ Serotype M1 ͉ epidemic waves ͉ ezrin F or most bacterial pathogens, there is relatively little understanding of why certain clonally related isolates cause abundant infections, whereas others do not. Molecular explanation of these phenomena is critical to development of rational methods to limit pathogen emergence, resurgence, and dissemination.Group A Streptococcus (GAS) is an important human pathogen that causes infections ranging from pharyngitis to necrotizing fasciitis and the postinfectious sequelae acute rheumatic fever and acute glomerulonephritis. GAS are genetically highly heterogeneous. For example, more than 150 distinct M-types have been identified on the basis of antigenic differences in the M protein, an antiphagocytic surface molecule that is an important virulence factor (1). However, GAS expressing relatively few M types cause the majority of human invasive infections. In particular, M1 strains are the most common serotype recovered from invasive disease episodes and also have a propensity to cause epidemics (2).Streptococcal inhibitor of complement (Sic) is a secreted protein produced by serotype M1 GAS that inhibits the formation of the membrane attack complex (MAC) of complement in vitro by binding to the C5b-C7 complex (3, 4). Sic production is necessary for per...