title: Structural Stability of Streptococcal Serum Opacity Factor.
abstract: Streptococcal serum opacity factor (SOF) is a protein that clouds the plasma of multiple mammalian species by disrupting high density lipoprotein (HDL) structure. Intravenous infusion of low dose SOF (4 µg) into mice reduces their plasma cholesterol concentrations ~ 40% in 3 h. Here we investigated the effects of pH, ionic strength, temperature, and denaturation with guanidinium chloride (GdmCl) on SOF stability and its reaction vs HDL. SOF stability was tested by pre-incubation of SOF at various temperatures, pH's, and GdmCl concentrations and measuring the SOF reaction rate at pH 7.4 and 37 °C. SOF retained activity at temperatures up to 58 °C, at pH 4 to 10, and in 8.5 M GdmCl after being returned to standard buffer conditions. The effects of GdmCl, pH, and ionic strength on the SOF reaction rates were also measured. SOF was inactive at GdmCl ≥ 1 M; SOF was most active at pH 5, near its isoelectric point and at an ionic strength of 3 (in NaCl). These data reveal that SOF is a stable protein and suggest that its activity is determined, in part, by the effects of pH and ionic strength on its overall charge relative to that of its reaction target, HDL.
authors.affiliation: The Center for Bioenergetics and Metabolism, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX, 77030, USA.
authors.forename: Dedipya
authors.initials: D
authors.lastname: Yelamanchili
authors.affiliation: The Center for Bioenergetics and Metabolism, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX, 77030, USA.|Department of Medicine, Weill Cornell Medicine, 1305 York Ave, New York, NY, 10021, USA.
authors.forename: Baiba K
authors.initials: BK
authors.lastname: Gillard
authors.affiliation: The Center for Bioenergetics and Metabolism, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX, 77030, USA.|Department of Medicine, Weill Cornell Medicine, 1305 York Ave, New York, NY, 10021, USA.
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Gotto
authors.affiliation: The Center for Bioenergetics and Metabolism, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX, 77030, USA.|Department of Medicine, Weill Cornell Medicine, 1305 York Ave, New York, NY, 10021, USA.
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Pownall
authors.affiliation: The Center for Bioenergetics and Metabolism, Houston Methodist Research Institute, 6670 Bertner St., Houston, TX, 77030, USA. crosales@houstonmethodist.org.|Department of Medicine, Weill Cornell Medicine, 1305 York Ave, New York, NY, 10021, USA. crosales@houstonmethodist.org.
authors.forename: Corina
authors.identifier: 0000-0002-9068-2775
authors.initials: C
authors.lastname: Rosales
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D004795:Enzyme Stability; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D010447:Peptide Hydrolases / Q000737:chemistry*; D000072417:Protein Domains; D013291:Streptococcus / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; C021908:opacity factor; D010447:Peptide Hydrolases
keywords: Cholesterol; High density lipoproteins; Protein stability; Serum opacity factor