Site-directed mutagenesis of streptococcal plasmin receptor protein (Plr) identifies the C-terminal Lys334 as essential for plasmin binding, but mutation of the plr gene does not reduce plasmin binding to group A streptococci.
Plasmin(ogen) binding is a common property of many pathogenic bacteria including group A streptococci. Previous analysis of a putative plasmin receptor protein, Plr, from the group A streptococcal strain 64/14 revealed that it is a glyceraldehyde-3-phosphate dehydrogenase and that the plr gene is present on the chromosome as a single copy. This study continues the functional characterization of Plr as a plasmin receptor. Attempts at insertional inactivation of the plr gene suggested that this single-copy gene may be essential for cell viability. Therefore, an alternative strategy was applied to manipulate this gene in vivo. Site-directed mutagenesis of Plr revealed that a C-terminal lysyl residue is required for wild-type levels of plasmin binding. Mutated Plr proteins expressed in Escherichia coli demonstrated reduced plasmin-binding activity yet retained glyceraldehyde-3-phosphate dehydrogenase activity. A novel integration vector was constructed to precisely replace the wild-type copy of the plr gene with these mutations. Isogenic streptococcal strains expressing altered Plr bound equivalent amounts of plasmin as wild-type streptococci. These data suggest that Plr does not function as a unique plasmin receptor, and underscore the need to identify other plasmin-binding structures on group A streptococci and to assess the importance of the plasminogen system in pathogenesis by inactivation of plasminogen activators and the use of appropriate animal models.
Division of Hematology/Oncology, Department of Medicine, University of Florida College of MedicineBox 100277, Gainesville, FL 32610-0277USA.
Scott B
SB
Winram
Division of Hematology/Oncology, Department of Medicine, University of Florida College of MedicineBox 100277, Gainesville, FL 32610-0277USA.
Richard
R
Lottenberg
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D005341:Fibrinolysin / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D008239:Lysine / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D018000:Receptors, Peptide / Q000235:genetics* / Q000378:metabolism; D013297:Streptococcus pyogenes / Q000235:genetics* / Q000378:metabolism
D001426:Bacterial Proteins; D010446:Peptide Fragments; D018000:Receptors, Peptide; C065181:plasmin receptor; D005341:Fibrinolysin; D008239:Lysine