Localization and characterization of the ligand-binding domain of the fibrinogen-binding protein (FgBP) of Streptococcus equi subsp. equi.
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 alpha-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 alpha-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 degrees C and is independent of Ca2+ ions. MS analysis provided corroborative evidence that FgBP is covalently linked to the cell wall peptidoglycan.
Meehan
Mary
M
National Pharmaceutical Biotechnology Centre, BioResearch, Ireland1, and Department of Microbiology, Moyne Institute of Preventive Medicine2, Trinity College, Dublin 2, Ireland.
Muldowney
Deirdre A
DA
National Pharmaceutical Biotechnology Centre, BioResearch, Ireland1, and Department of Microbiology, Moyne Institute of Preventive Medicine2, Trinity College, Dublin 2, Ireland.
Watkins
Naomi J
NJ
National Pharmaceutical Biotechnology Centre, BioResearch, Ireland1, and Department of Microbiology, Moyne Institute of Preventive Medicine2, Trinity College, Dublin 2, Ireland.
Owen
Peter
P
National Pharmaceutical Biotechnology Centre, BioResearch, Ireland1, and Department of Microbiology, Moyne Institute of Preventive Medicine2, Trinity College, Dublin 2, Ireland.
D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D008024:Ligands; D008322:Mammals; D008970:Molecular Weight; D010457:Peptidoglycan / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D013045:Species Specificity; D018502:Streptococcus equi / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D002352:Carrier Proteins; D005353:Fibronectins; D008024:Ligands; D010457:Peptidoglycan; D011994:Recombinant Proteins; C112406:fibrinogen-binding protein, Streptococcus equi