title: A study of phenylalanine side-chain dynamics in surface-adsorbed peptides using solid-state deuterium NMR and rotamer library statistics.
abstract: Extracellular matrix proteins adsorbed onto mineral surfaces exist in a unique environment where the structure and dynamics of the protein can be altered profoundly. To further elucidate how the mineral surface impacts molecular properties, we perform a comparative study of the dynamics of nonpolar side chains within the mineral-recognition domain of the biomineralization protein salivary statherin adsorbed onto its native hydroxyapatite (HAP) mineral surface versus the dynamics displayed by the native protein in the hydrated solid state. Specifically, the dynamics of phenylalanine side chains (viz., F7 and F14) located in the surface-adsorbed 15-amino acid HAP-recognition fragment (SN15: DpSpSEEKFLRRIGRFG) are studied using deuterium magic angle spinning ((2)H MAS) line shape and spin-lattice relaxation measurements. (2)H NMR MAS spectra and T1 relaxation times obtained from the deuterated phenylalanine side chains in free and HAP-adsorbed SN15 are fitted to models where the side chains are assumed to exchange between rotameric states and where the exchange rates and a priori rotameric state populations are varied iteratively. In condensed proteins, phenylalanine side-chain dynamics are dominated by 180° flips of the phenyl ring, i.e., the "π flip". However, for both F7 and F14, the number of exchanging side-chain rotameric states increases in the HAP-bound complex relative to the unbound solid sample, indicating that increased dynamic freedom accompanies introduction of the protein into the biofilm state. The observed rotameric exchange dynamics in the HAP-bound complex are on the order of 5-6 × 10(6) s(-1), as determined from the deuterium MAS line shapes. The dynamics in the HAP-bound complex are also shown to have some solution-like behavioral characteristics, with some interesting deviations from rotameric library statistics.
authors: Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195, United States.
authors: Kun
authors: K
authors: Li
authors: Prashant S
authors: PS
authors: Emani
authors: Jason
authors: J
authors: Ash
authors: Michael
authors: M
authors: Groves
authors: Gary P
authors: GP
authors: Drobny
mesh_terms: D000327:Adsorption; D000465:Algorithms; D018441:Biofilms; D003198:Computer Simulation; D017886:Durapatite / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009038:Motion; D010455:Peptides / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry*; D017433:Protein Structure, Secondary; D012463:Saliva / Q000378:metabolism; D012471:Salivary Proteins and Peptides / Q000737:chemistry*; D012996:Solutions; D013499:Surface Properties
chemical_list: D010455:Peptides; C018149:STATH protein, human; D012471:Salivary Proteins and Peptides; D012996:Solutions; D010649:Phenylalanine; D017886:Durapatite