However, the physiological and pathological significance of the interaction remains to be elucidated. High-density lipoprotein (HDL), one of the major lipoproteins, enables lipids such as cholesterol and triglycerides to be reversely transported. A high level of HDL-associated cholesterol seems to protect against cardiovascular diseases (Kapur et al., 2008). It has also been demonstrated

that HDL may participate in innate immunity by protecting against some infections (Grunfeld & Feingold, 2008). When infection and inflammation induce the acute-phase response, the level of HDL in plasma is decreased (Khovidhunkit et al., 2004). HDL can bind the endotoxin (lipopolysaccharide) of Gram-negative bacteria and LTA Pirfenidone research buy of Gram-positive bacteria, and neutralize their toxic effects (Grunfeld et al., 1999; Khovidhunkit et al., 2004). In addition, HDL possesses a broad antiviral activity (Singh et al., 1999). Notably, trypanosoma lytic factors, one subset of HDL, protect humans from Trypanosoma brucei (Raper et al., 2001) and Leishmania infections (Samanovic et al., 2009). Interestingly, the serum GSK J4 clinical trial opacity factor (SOF) expressed by class II GAS strains interacts with ApoAI and ApoAII of HDL, subsequently causing the disrupture of HDL, which may attenuate the anti-inflammatory functions of HDL and contribute to the pathogenesis of GAS infection (Courtney

et al., 2006). The present study demonstrates that Scl1 from M41-type GAS ATCC12373 specifically binds HDL. The

interaction mechanism was also studied. Two strains of GAS, M6 (CMCC32175, obtained from the China Medical Culture Collection Center) and M41 (ATCC12373, obtained from the American Type Culture Collection), were used in this study. Cultivation of GAS was performed as reported previously (Han et al., 2006a, b). The GAS was grown in Todd–Hewitt broth (Becton, Dickinson and Company, MD) supplemented with 0.2% yeast extract (Oxoid, Hampshire, England) (THY medium). Nutrient broth agar containing 5% sheep blood was used as a solid medium. GAS was incubated in THY broth, 5% CO2, 37 °C to the Urocanase mid-logarithmic phase (OD600 nm∼0.5). GAS cells were collected by centrifugation at 6000 g for 10 min at 4 °C, and the cell pellet was washed twice with PBSA [phosphate-buffered saline (PBS) containing 0.02% NaN3], and the GAS cell suspensions in PBSA were used for the following experiments. Escherichia coli was grown at 37 °C in Luria–Bertani (LB) broth (tryptone 10 g L−1, yeast extract 5 g L−1 (Oxoid), and LB agar was used as a solid medium. Ampicillin (100 μg−1 mL) (Bio Basic Inc., ON, Canada) and 0.2 μg mL−1 anhydrotetracycline (IBA-GmbH, Göttingen, Germany) were used as selection markers. Recombinant Scls (rScl) were produced in E. coli using the Strep-tag II expression and purification system (IBA-GmbH), as described previously (Xu et al., 2002; Han et al., 2006b).