A strain of Streptococcus sanguis that induced rabbit platelets to aggregate in vitro (Agg+ phenotype) was hypothesized to be a more virulent pathogen than an Aggstrain in experimental endocarditis in rabbits. A left ventricular catheter was implanted, and then an Agg+ or Aggstrain was inoculated intravenously. Vegetations formed on the aortic semilunar valves but were unaffected by the duration of implantation of the catheter. Vegetations enlarged by accumulating platelets and their mass increased directly with the duration of endocarditis. Inoculation of the Agg+ strain consistently caused endocarditis with significantly larger vegetations, a more severe clinical course (including febrile episodes, hematological changes, and signs of myocardial ischemia), more gross lesions in major organs, and greater mortality than inoculation with the Agg-strain, saline, or the Agg+ strain pretreated with monospecific rabbit immunoglobulin G or Fab fragments against its platelet aggregation-associated protein (PAAP; class II). In experimental endocarditis, PAAP expressed by Agg+ S. sanguis appeared to be an important virulence factor.INFECT. IMMUN. M.on July 10, 2020 by guest http://iai.asm.org/ Downloaded from

Certain strains of Streptococcus sanguis adhere (Adh+) selectively to human platelets and, in plasma, induce them to aggregate (Agg+) into in vitro thrombi. In this study, we examined 18 recent endocarditis and dental plaque isolates of microorganisms that were biotyped as S. sanguis for coexpression of platelet interactivity phenotypes with another possible virulence factor in bacterial endocarditis, dextran synthesis. Detectable production of extracellular glucosyltransferase ranged from 0.2 to 66 mU/mg of culture fluid for 10 representative strains tested. Production of extracellular or cell-associated glucosyltransferase, fructosyltransferase, and soluble or insoluble dextrans was not necessarily coexpressed with platelet interactivity phenotypes, since the levels of production of soluble and insoluble dextrans varied among representative Adh+ Agg+ and Adh-Aggstrains. Analysis of a second panel of 38 fresh dental plaque isolates showed that S. sanguis distributes in a reproducible manner into the possible phenotype groups. Strains with different platelet interactivity phenotypes were distinguished with a panel of four murine monoclonal antibodies (MAbs) raised against Adh+ Agg+ strain 133-79 and screened to rule out artifactual reactions with antigenic components in culture media. The MAbs reacted selectively with Adh+ Agg+ strains in a direct-binding, whole-cell, enzyme-linked immunosorbent assay and also inhibited their interactions with platelets. Analysis of minimal tryptic digests of many strains, including variants that failed to bind the MAbs, suggested that some noninteractivity phenotypes possess cryptic surface determinants. Since the ability to adhere to platelets and induce them to aggregate is relatively stable, these traits may be useful in a phenotyping scheme for these Lancefield nontypeable streptococci.

Protein tyrosine phosphatases 1B (PTP1B) is a major negative regulator of both insulin and leptin signaling pathways. In view of this, it becomes an important target for drug development against cancers, diabetes and obesity. The aim of the current study is to use the long time-scale molecular dynamics (MD) simulations to investigate the structural and dynamic factors that cause its inhibition by INTA and INTB, the two most potent and highly selective PTP1B inhibitors known so far. In order to investigate the mode of collective motions that is vitally important to the biological function, the covariance matrix of C(alpha) atoms was introduced for performing the dynamic analysis of the inhibition systems. It has been observed that the conformational and dynamic features of WPD-Loop, R-Loop and S-Loop play a key role in providing a smooth entrance for the inhibitors moving into the binding pocket as well as a favorable microenvironment to stabilize them. Furthermore, the hydrogen bonding networks formed around the active site with INTA and INTB may be the main reason of why the inhibition of PTP1B by the two ligands is so potent and selective. All these findings might provide useful insights for developing novel and effective drugs to treat cancer, diabetes and obesity.

Teeth in the oral cavity are coated with a salivary film or pellicle, which lacks apparent intermolecular organization. This heterogeneous film facilitates binding of early commensal colonizing bacteria, including Streptococcus sanguis. To test the hypothesis that sufficient intermolecular organization exists in salivary films to form binding sites for S. sanguis, an in vitro model of saliva-coated teeth was probed with murine anti-idiotypical monoclonal antibodies (mAb2, anti-ids). The anti-ids were harvested from hybridomas that were developed in response to first generation murine hybridomas that produced anti-S. sanguis adhesin monoclonal antibodies (mAb1). The anti-ids (i) reacted with experimental salivary films and inhibited S. sanguis adhesion in a dose-dependent fashion. In Western blots, the anti-ids (ii) recognized a high molecular weight salivary antigen and (iii) secretory IgA (sIgA) light chain and ␣-amylase. After isolation by gel filtration from whole saliva or mixed secretory IgA and ␣-amylase, the high molecular weight component, containing amylase activity and sIgA, bound to hydroxyapatite to promote adhesion of S. sanguis. Therefore, a complex enriched in secretory immunoglobulin A and ␣-amylase forms a S. sanguis-binding site.

By mimicking hemostatic structural domains of collagen,Streptococcus sanguis (aggregation-positive phenotype; Agg+) induces platelets to aggregate in vitro. To test the hypothesis that aggregation occurs in vivo, S. sanguis(Agg+ or Agg− suspension) was infused intravenously into rabbits. The extent of hemodynamic and cardiopulmonary changes and the fate of circulating platelets were Agg+ strain dose dependent. Within 45 to 50 s of the start of infusion, 40 × 108 CFU of the Agg+ strain caused increased blood pressure. Thirty seconds after infusion, other changes occurred. Intermittent electrocardiographic abnormalities (13 of 15 rabbits), ST-segment depression (10 of 15 rabbits), and preventricular contractions (7 of 15 rabbits) manifested at 3 to 7 min, with frequencies dose dependent. Respiratory rate and cardiac contractility increased during this phase. Blood catecholamine concentration, thrombocytopenia, accumulation of111Indium-labeled platelets in the lungs, and ventricular axis deviation also showed dose dependency. Rabbits were unaffected by inoculation of an Agg− strain. Therefore, Agg+ S. sanguis induced platelet aggregation in vitro. Platelet clots caused hemodynamic changes, acute pulmonary hypertension, and cardiac abnormalities, including ischemia.