Bound water in apo and hole bovine heart fatty-acid-binding protein determined by heteronuclear NMR spectroscopy

Two-and three-dimensional heteronuclear NMR experiments have been performed to identify internally bound water molecules in the solution structure of bovine heart fatty-acid-binding protein (heart FABP). NOE and rotating-frame NOE (ROE) cross peaks between protein protons and protons of bound water molecules were observed in two-dimensional H2O-ROE/NOE-H-1,N-15-heteronuclear single quantum coherence spectra recorded from a uniformly C-13/N-15-enriched sample of bovine heart FABP. Contacts between water protons and 23 NH protons of the protein backbone were identified. The protein structure consists of 10 antiparallel beta-strands (beta A - beta J), forming two nearly orthogonal beta-sheets, and a short helix-turn-helix motif connecting beta-strands A and B. The spatial folding resembles a beta-barrel. Most of the water molecules are localized in the gap between beta-strands D and E, and near the two alpha-helices. In the delipidated heart FABP additional contacts between water molecules and NH protons could be observed using a three-dimensional rotating frame Overhauser H-1,N-15 heteronuclear single quantum coherence experiment obtained with a N-15-labeled sample of apo-heart FABP.