The rethylesterse CheB from S almonelia typhntninnm. is a protein in volved in the reversible covalenl modification of tran.srnembrane ehonmrcttors. ChoH ralHly/fs ilif dcmetbvUrion of methylclutdniato side chains introdired governing pH dependent conformations! changes in the molecule. To rharacienJ.e t he effe.cts of phosphorylation. pH and calcium binding on the con formation, and stability of a casein, fluorescence pectrospcopv and Circular Dichroism have been used to investigate the local environment of the two trypîophan residues and the overall secondary structure of the molecule. Conipar ison of phosphorylated and dephos[)horylated a casein show a blue shift in one tryploplian, indicating a more compact local environment in the dephospho rvlated form. Calcium and decreased pH induce similar fluorescence changes Miggest ing that charge effects due to phosphorylat ion control the conformation of the molecule. CD spectra of phosphorylated and dephosphorylated isoforms how conformational changes of o Casein caused by phosphorylation at 20.r>nrn and 220nm at pH H.O. Calcium affects the helical region at 220nm and the .1 strand region at 205nm. At pH 5.0 and pH r>.5. phosphorvlatfld and dephoi pliorylated o Casein both aggregate. Circular dic.hroism studies of the effect of trypsin cleravage showed that o helical regions are cleaved first, followed by ,i strand regions.The combination of the fluorescence and CD studies al low for a model of conformational changes in n casein which accounts for how phosphorylation governs pH and calcium induced changes in structure.
|Published - 1997
All Science Journal Classification (ASJC) codes
- Molecular Biology