title: Side chain dynamics monitored by 13C-13C cross-relaxation.
abstract: A method to measure (13)C-(13)C cross-relaxation rates in a fully (13)C labeled protein has been developed that can give information about the mobility of side chains in proteins. The method makes use of the (H)CCH-NOESY pulse sequence and includes a suppression scheme for zero-quantum (ZQ) coherences that allows the extraction of initial rates from NOE buildup curves. The method has been used to measure (13)C-(13)C cross-relaxation rates in the 269-residue serine-protease PB92. We focused on C(alpha)-C(beta) cross-relaxation rates, which could be extracted for 64% of all residues, discarding serine residues because of imperfect ZQ suppression, and methyl (13)C-(13)C cross-relaxation rates, which could be extracted for 47% of the methyl containing C-C pairs. The C(alpha)-C(beta) cross-relaxation rates are on average larger in secondary structure elements as compared to loop regions, in agreement with the expected higher rigidity in these elements. The cross-relaxation rates for methyl containing C-C pairs show a general decrease of rates further into the side chain, indicating more flexibility with increasing separation from the main chain. In the case of leucine residues also long-range C(beta)-C(delta) cross-peaks are observed. Surprisingly, for most of the leucines a cross-peak with only one of the methyl C(delta) carbons is observed, which correlates well with the chi(2) torsion-angle and can be explained by a difference in mobility for the two methyl groups due to an anisotropic side chain motion.
authors.affiliation: Bijvoet Center for Biomolecular Research, NMR Spectroscopy, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Klaartje
authors.initials: K
authors.lastname: Houben
authors.forename: Rolf
authors.initials: R
authors.lastname: Boelens
mesh_terms: D002247:Carbon Isotopes / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011487:Protein Conformation
chemical_list: D002247:Carbon Isotopes