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Biomedical subjects

Steven Baker

Publications and source records attributed to Steven Baker.

5 recordsLinked to original sources
PubMed2006

Factor XIIIa mediated attachment of S. aureus fibronectin-binding protein A (FnbA) to fibrin: identification of Gln103 as a major cross-linking site.

In the present study we investigated the role of factor XIIIa reactive Gln and Lys sites of staphylococcal FnbA receptor in cross-linking reaction with alpha chains of fibrin. For this purpose we produced two recombinant FnbA mutants in which either a single Gln103 site (1Q FnbA) or all identified reactive Gln103, 105, 783, 830 and Lys157, 503, 620, 762 sites (4Q4K FnbA) were substituted with Ala residues. The results of FXIIIa-catalyzed incorporation of dansylcadaverine and dansylated peptide patterned on the NH2-terminal segment of fibronectin revealed that the reactivity of Gln substrate sites was drastically reduced in 1Q FnbA and 4Q4K FnbA mutants, while the reactivity of Lys substrate sites was only moderately decreased in 4Q4K FnbA. When it was tested in the FXIIIa-mediated fibrin cross-linking reaction, the 1Q FnbA mutant exhibited about 70-85% reduction in reactivity compared to that of the wild-type FnbA. These results demonstrate that FnbA participates in cross-linking to alpha chains of fibrin predominantly via its Gln103 reactive site. Several minor sites, including residues replaced in 4Q4K FnbA mutant, contributed to an additional 15-30% of the total fibrin cross-linking reactivity of FnbA. Comparison of amino acid sequences that follow the major reactive Gln site in FnbA and several known substrate proteins revealed that FXIIIa displays a preference for the glutamine residue in an xQAxBxPx sequence, where Q represents reactive glutamine, x is any amino acid residue, A is a polar residue, B is either valine or leucine, and P is proline.

Adhesins, Bacterial↗
PubMed2003

Staphylococcus aureus fibronectin-binding protein serves as a substrate for coagulation factor XIIIa: evidence for factor XIIIa-catalyzed covalent cross-linking to fibronectin and fibrin.

In this study, we have investigated the interactions of a Staphylococcal recombinant fibronectin-binding protein A (rFnbA) with fibronectin, fibrinogen, and fibrin. Using analytical size-exclusion chromatography, we evaluated the stoichiometry of reversible binding of FnbA to fibronectin and demonstrated that, in solution, it can accommodate at least two molecules of fibronectin. Results of ELISA experiments demonstrated that rFnbA binds with equally high affinity to both immobilized fibrinogen and fibrin. When included into a thrombin-induced fibrin polymerization reaction, rFnbA strongly inhibited fibrin assembly in a dose-dependent manner. In this study, we have shown that rFnbA can act as a substrate for coagulation factor XIIIa. Factor XIIIa catalyzes the incorporation of amine donor (dansylacadaverine) and amine acceptor (peptide patterned on the N-terminal sequence of fibronectin) synthetic probes into rFnbA, suggesting that it serves as a bifunctional substrate containing reactive glutamine and lysine residues. We have demonstrated that the reversible complex formed by rFnbA and fibronectin or rFnbA and fibrin is covalently stabilized by the transglutaminase action of factor XIIIa. Incubation of rFnbA in the presence of either of its ligands and factor XIIIa results in the introduction of intermolecular epsilon-(gamma-glutamyl)lysine isopeptide bond(s) and the formation of high molecular mass heteropolymers. These findings suggest a novel mechanism by which pathogenic Staphylococcus aureus may utilize the transglutaminase activity of factor XIIIa for attachment to soluble proteins, cell surfaces, and matrixes.

Adhesins, Bacterial↗
PubMed2003

Comparative analysis of the genome sequences of Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica.

Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica are closely related Gram-negative beta-proteobacteria that colonize the respiratory tracts of mammals. B. pertussis is a strict human pathogen of recent evolutionary origin and is the primary etiologic agent of whooping cough. B. parapertussis can also cause whooping cough, and B. bronchiseptica causes chronic respiratory infections in a wide range of animals. We sequenced the genomes of B. bronchiseptica RB50 (5,338,400 bp; 5,007 predicted genes), B. parapertussis 12822 (4,773,551 bp; 4,404 genes) and B. pertussis Tohama I (4,086,186 bp; 3,816 genes). Our analysis indicates that B. parapertussis and B. pertussis are independent derivatives of B. bronchiseptica-like ancestors. During the evolution of these two host-restricted species there was large-scale gene loss and inactivation; host adaptation seems to be a consequence of loss, not gain, of function, and differences in virulence may be related to loss of regulatory or control functions.

Base Sequence↗
PubMed2002

Hematopoietic stem cell transplantation for severe and refractory lupus. Analysis after five years and fifteen patients.

OBJECTIVE: To determine the safety and long-term efficacy of immune ablation and autologous hematopoietic stem cell transplantation (HSCT) in severe systemic lupus erythematosus (SLE). METHODS: Fifteen patients with persistently active SLE after intravenous (IV) cyclophosphamide (CYC) therapy underwent HSCT. Stem cells were mobilized with CYC (2.0 gm/m(2)) and granulocyte colony-stimulating factor (5 microg/kg/day). Lymphocytes were depleted from the graft by selection of CD34-positive cells. The conditioning regimen used was CYC (200 mg/kg), antithymocyte globulin (90 mg/kg), and methylprednisolone (3 mg/kg). Outcome was evaluated by the SLE Disease Activity Index (SLEDAI), serum complement levels, serologic features, function of diseased organs, and immunosuppressive medication requirements. RESULTS: Fifteen patients with persistent, severe SLE, 7 of whom were critically ill, were treated. No deaths occurred following treatment. The median followup after HSCT has been 36 months (range 12-66 months). All patients demonstrated a gradual, but marked, improvement. The SLEDAI score has declined to 1 year after HSCT, 10 have discontinued immunosuppressive medications, and the prednisone dosage has been tapered to 15 mg/day in 1. Only 2 patients have demonstrated clinical evidence of recurrence of active lupus. One of these patients currently requires no immunosuppressive medication and has a normal performance status. The other patient is currently receiving IV CYC. CONCLUSION: In patients experiencing the persistence of organ-threatening lupus following standard, aggressive therapy, HSCT may be performed safely, with marked improvement and sustained withdrawal of all immunosuppressive medication for most patients. A phase III randomized trial is warranted to determine the relative efficacy and durability of remission of HSCT compared with standard therapies.

Adolescent↗