Two Modes of Ligand Binding in Maltose-binding Protein ofEscherichia coli: ELECTRON PARAMAGNETIC RESONANCE STUDY OF LIGAND-INDUCED GLOBAL CONFORMATIONAL CHANGES BY SITE-DIRECTED SPIN LABELING

摘要: Abstract Binding of ligands to the maltose-binding protein (MBP) Escherichia coli often causes a global conformational change involving closure its two lobes. We have introduced cysteine residue onto each these lobes by site-directed mutagenesis and modified residues with spin labels. Using EPR spectroscopy, we examined changes, caused ligand binding, in distance between labels, hence The binding both maltose maltotetraose induced considerable N- C-terminal MBP. Little occurred upon maltotetraitol or β-cyclodextrin. Previous study fluorescence UV differential absorbance spectroscopy (Hall, J. A., Gehring, K., Nikaido, H. (1997) Biol. Chem. 272, 17605–17609) showed that large portion bound MBP via one mode (R “end-on” mode), which is physiologically active leads subsequent transport across cytoplasmic membrane. In contrast, β-cyclodextrin different (B “middle” inactive. present work suggests B nonproductive because this manner prevent domains MBP, and, as result, resulting ligand-MBP complex incapable interacting properly inner membrane-associated transporter complex.