Localization and characterization of the ligand-binding domain of the fibrinogen-binding protein (FgBP) of Streptococcus equi subsp. equi

• Published in: Microbiology (Society for General Microbiology) 2000-05, Vol.146 (5), p.1187-1194
• Main Authors: Meehan, Mary, Muldowney, Deirdre A, Watkins, Naomi J, Owen, Peter
• Format: Article
• Language: English
• Subjects: Animals; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Carrier Proteins - chemistry; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Wall - metabolism; Cloning, Molecular; Escherichia coli - genetics; FgBP protein; Fibrinogen; Fibronectins - metabolism; Fundamental and applied biological sciences. Psychology; Genetics; Humans; Immunoblotting; Ligands; Mammals; Microbiology; Molecular Weight; Peptidoglycan - metabolism; Peptidoglycans; Protein Binding; Protein Structure, Secondary; Recombinant Proteins - chemistry; Species Specificity; Streptococcus equi; Streptococcus equi - genetics; Streptococcus equi - metabolism
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/00221287-146-5-1187

National Pharmaceutical Biotechnology Centre, BioResearch, Ireland 1 , and Department of Microbiology, Moyne Institute of Preventive Medicine 2 , Trinity College, Dublin 2, Ireland Author for correspondence: Peter Owen. Tel: [phone]. Fax: [phone]. e-mail: powen{at}tcd.ie The group C streptococcus Streptococcus equi subsp. equi possesses a 498-residue major cell-wall-associated protein (FgBP) which binds horse fibrinogen (Fg), reacts with convalescent horse serum and protects against lethal S. equi challenge in a small animal model. In the present study, analysis of a panel of 17 purified N- and C-terminal FgBP truncates by ligand affinity blotting and SDS-PAGE revealed that the region required for maximum binding of Fg extended over the first half of the mature protein. The C-terminal two-thirds of this domain is predicted to be -helical coiled-coil and the N-terminal one-third to possess non-coiled-coil single strands. Residues at the extreme N-terminus and within the coiled-coil region are both required for ligand binding. A high incidence of -helical coiled-coil structure also seems to be responsible in part for the aberrant mobility of FgBP on SDS gels. The efficiency with which FgBP binds Fg from different animal species decreases in the order horse>mouse, pig>rat>sheep, dog, bovine, human. Binding to horse Fg is inversely related to temperature over the range 45–4 °C and is independent of Ca 2+ ions. MS analysis provided corroborative evidence that FgBP is covalently linked to the cell wall peptidoglycan. Keywords: Streptococcus equi subsp. equi , fibrinogen-binding protein, ligand-binding domain Abbreviations: CD, circular dichroism; Fg, fibrinogen; FgBP, fibrinogen-binding protein; MALDI-TOF, matrix-assisted laser desorption/ionization time-of-flight