A high-resolution solid-state 13C-NMR study on [1-13C]Ala and [3-13C]Ala and [1-13C]Leu and Val-labelled bacteriorhodopsin. Conformation and dynamics of transmembrane helices, loops and termini, and hydration-induced conformational change.

摘要: We have recorded 100.7-MHz high-resolution solid-state 13C-NMR spectra of [3-13C]Ala, [1-13C]Ala-labelled, Leu-labelled and Val-labelled bacteriorhodopsin (bR), to analyze the conformation dynamics transmembrane alpha helices hydration-induced conformational changes. assigned signals these 13C-labelled amino acid residues portions helices, loops N-terminus C-terminus, based on conformation-dependent 13C chemical shift. The assignment peaks is straightforward in view characteristic shifts C beta carbonyl carbons, referred data model system. were further divided into three or four which are ascribed either a dispersion torsion angles variation environments around helices. In addition, we found that C-terminus bR virtually random-coil form undergoes rapid reorientational motion hydrated Further, show higher-order (secondary and/or tertiary) structure influenced by hydration/dehydration process purple membrane, as viewed from peak profile Ala signals. This change occurs between relative humidities 2% 4%, consistent with shift absorption maxima retinal, arise protonation/deprotonation processes Schiff base. contrast, no such for Leu, Val residues. For latter two residues, some spectral changes noted at stage full hydration.