A study Of ora| streptococcal histone-like protein and virulence mechanism

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Streptococcus intermedius is associated with endogenous infections leading to abscesses in the oral cavity and deep-seated sites, such as the brain and liver. Histone-like protein (HLP), which binds to DNA and RNA molecules and to lipoteichoic acid and epithelial cells, is well conserved among bacterial species and induces macrophages to produce interleukin (IL)-1 and tumor necrosis factor (TNF)-α. In this study, we cloned the gene encoding S. intermedius HLP (HLPSi) from chromosomal DNA by use of the polymerase chain reaction (PCR) using the primers based on S. pyogenes hip gene and ligated to the glutathione S-transferase (GST) fusion vector. The encoded HLPSi had 91 amino acids; and its molecular weight and isoelectric point calculated from the sequence were 9,603 and 10.21 , respectively. The sequence of HLPSi had a high identity with those sequences of the HLP of S. pyogenes A374 and Staphylococcus aureus Mu50 and showed high homology with a 21 -kDa molecule of Mycobavterium leprae (ML-LBP21) at the amino acid level. The immunoelectron micrograph of S. intermedius by anti-HLPSi antibody and ELISA demonstrated that a part of HLPSi was localized on the cell surface and that recombinant HLPSi (rHLPSi) bound to heparin. Our results suggest that HLP produced from bacterial cells may play various roles in pathogenesis by helping the bacteria to bind to their target tissue within the infected host and may contribute to tissue injury at the infection site.