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Thermodynamic Analysis of the Interaction Between O‐Acetylserine Sulfhydrylase and the C‐Terminal Peptide of Serine Acetyltransferase
Author(s) -
Kumaran Sangaralingam,
Jez Joseph M
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a644-c
Subject(s) - isothermal titration calorimetry , chemistry , cooperativity , peptide , dimer , cooperative binding , cysteine , enthalpy , serine , biochemistry , binding site , thermodynamics , enzyme , organic chemistry , physics
To understand how the C‐terminus of serine acetyltransferase (SAT) interacts with O‐acetylserine sulfhydrylase (OASS) in the plant cysteine synthase complex, we analyzed the thermodynamics of binding as a function of temperature and salt concentration using fluorescence spectroscopy and isothermal titration calorimetry (ITC). Our results suggest that 95% of the total binding energy in the complex may be contributed to the SAT C‐terminus (C10 peptide). The stoichiometry of OASS·C10 peptide complex formation is 2:1 over a range of temperatures (10 – 35 °C) and NaCl concentrations (20 – 500 mM), although the two binding sites of the OASS dimer exhibit different affinities depending upon temperature. ITC studies show that the relative contributions of entropy and enthalpy for binding also depended on temperature, as was cooperativity between the OASS subunits upon binding the C10 peptide. The heat capacity change and salt‐dependence studies suggest that hydrophobic interactions are likely to be involved in mediating the protein‐peptide interaction and for determining the binding specificity. The present study expands our understanding of cysteine synthase complex formation.