The serine-rich repeat (SRR) glycoproteins are a large family of adhesins found in many Gram-positive bacteria. These surface components are important virulence determinants for a broad range of human infections. GspB is an SRR adhesin of Streptococcus gordonii that mediates binding to human platelets through its interaction with the trisaccharide sialyl-T antigen (sTa) on the platelet receptor GPIb. This binding appears to be important for the pathogenesis of infective endocarditis, since mutagenesis of the GspB binding region results in decreased platelet binding in vitro, and reduced virulence in an animal model of this disease. Three properties of GspB binding may be highly important for the targeting of streptococci to the endocardium: affinity, selectivity, and fow enhancement. First, the binding of GspB to its platelet receptor is a high affinity interaction (KD 2.4 x 10-8 M). Second, GspB has a very selective binding spectrum, with sTa being its principal ligand. Third, GspB-mediated binding by bacteria to sTa is enhanced by levels of fluidic shear flow similar to those within the endovascular system. In combination, these three binding properties may target blood-borne streptococci to platelets immobilized at sites of endocardial injury (thereby initiating infection). GspB-mediated binding may also contribute to the subsequent formation of macroscopic endocardial lesions (vegetations) containing bacteria and platelets. This project seeks to define the molecular basis for GspB binding affinity, selectivity, and flow enhancement, and the relative importance of these properties for virulence.
Aim 1 will examine how the molecular architecture of the GspB binding domain confers affinity and selectivity. We will determine the structure of the GspB binding region cocrystallized with sTa and related compounds, select key domains and residues for targeted mutagenesis, and examine the impact of these mutations on binding affinity and selectivity. Two GspB homologs (Hsa and SrpA) that differ in their binding properties will also be evaluated.
Aim 2 will determine the structural features of GspB that contribute to flow-enhanced binding, and whether binding occurs via the formation of catch bonds. We will specifically examine the contribution of the serine-rich repeat domains of GspB in flow-enhanced binding.
Aim 3 will assess the impact of ligand affinity, selectivity and flow-enhanced binding on the pathogenesis of infective endocarditis. Isogenic variants of S. gordonii strain M99 that differ in their ligand binding properties will be compared for relative virulence, using a well-established co-infection model of this disease. This project will provide significant insights into the structural basis for carbohydrate binding by this novel group of bacterial adhesins, as well as the mechanisms for streptococcal binding to human platelets. In addition, these studies could provide a basis for novel therapies for infective endocarditis that target SRR glycoprotein binding.

Public Health Relevance

A key step in the development of many infections is the attachment of microbes onto host tissues. This research examines how bacteria known as streptococci attach to cardiac valves, leading to infection (endocarditis). By examining a central mechanism for producing this disease, this work will provide important mechanistic insights that may lead to novel antimicrobial therapies.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
GU, Xin-Xing
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Northern California Institute Research & Education
San Francisco
United States
Zip Code
Tso, Shih-Chia; Chen, Qiuyan; Vishnivetskiy, Sergey A et al. (2018) Using two-site binding models to analyze microscale thermophoresis data. Anal Biochem 540-541:64-75
Bensing, Barbara A; Li, Qiongyu; Park, Dayoung et al. (2018) Streptococcal Siglec-like adhesins recognize different subsets of human plasma glycoproteins: implications for infective endocarditis. Glycobiology 28:601-611
Yakovenko, Olga; Nunez, Jamie; Bensing, Barbara et al. (2018) Serine-Rich Repeat Adhesins Mediate Shear-Enhanced Streptococcal Binding to Platelets. Infect Immun 86:
Johnson, Keith C; Thomas, Wendy E (2018) How Do We Know when Single-Molecule Force Spectroscopy Really Tests Single Bonds? Biophys J 114:2032-2039
Starbird, C A; Perry, Nicole A; Chen, Qiuyan et al. (2018) The Structure of the Bifunctional Everninomicin Biosynthetic Enzyme EvdMO1 Suggests Independent Activity of the Fused Methyltransferase-Oxidase Domains. Biochemistry 57:6827-6837
Lin, Shun-Mei; Jang, A-Yeung; Zhi, Yong et al. (2017) Vaccination With a Latch Peptide Provides Serotype-Independent Protection Against Group B Streptococcus Infection in Mice. J Infect Dis 217:93-102
Garcia-de-la-Maria, C; Xiong, Y Q; Pericas, J M et al. (2017) Impact of High-Level Daptomycin Resistance in the Streptococcus mitis Group on Virulence and Survivability during Daptomycin Treatment in Experimental Infective Endocarditis. Antimicrob Agents Chemother 61:
Mishra, Nagendra N; Tran, Truc T; Seepersaud, Ravin et al. (2017) Perturbations of Phosphatidate Cytidylyltransferase (CdsA) Mediate Daptomycin Resistance in Streptococcus mitis/oralis by a Novel Mechanism. Antimicrob Agents Chemother 61:
Seepersaud, Ravin; Sychantha, David; Bensing, Barbara A et al. (2017) O-acetylation of the serine-rich repeat glycoprotein GspB is coordinated with accessory Sec transport. PLoS Pathog 13:e1006558
Yim, Juwon; Smith, Jordan R; Singh, Nivedita B et al. (2017) Evaluation of daptomycin combinations with cephalosporins or gentamicin against Streptococcus mitis group strains in an in vitro model of simulated endocardial vegetations (SEVs). J Antimicrob Chemother 72:2290-2296

Showing the most recent 10 out of 16 publications