High-resolution proton magnetic resonance study of porcine colipase and its interactions with taurodeoxycholate

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Abstract
A high-resolution 270-MHz proton NMR study of procine colipase I was performed and the resonances in the aromatic region of the spectrum were assigned to amino acid residues by pH titration and decoupling experiments. The apparent pKa values of the 3 tyrosines were 10.2, 10.3 and 11.8, with one of the tyrosines having properties of a buried residue. A tentative assignment to the amino acid residues in the primary sequence of colipase was discussed. The effects of taurodeoxycholate (TDC) and a postively charged deoxycholate derivative on the aromatic region of the colipase NMR spectrum indicate that all tyrosines and 1 histidine are affected by the bile-salt binding, suggesting that the TDC molecules bind near these residues to a hydrophobic region on colipase. Measurements and calculations on the line width of the C(18) methyl group resonance suggest that the line-width increase of this resonance upon interaction of TDC with colipase to a large extent can be explained as due to the slower tumbling of the TDC molecules bound to colipase.

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