CONFORMATION AND DYNAMICS OF MEMBRANE-PROTEINS AND BIOLOGICALLY-ACTIVE PEPTIDES AS STUDIED BY HIGH-RESOLUTION SOLID-STATE C-13 NMR

We have explored an empirical approach to clarify the three-dimensiona l structure and dynamics of membrane proteins such as bacteriorhodopsi n (bR) based on C-13 NMR measurements, utilizing the concept of the co nformation-dependent displacements of C-13 chemical shifts as determin ed by cross polarization-magic angle spinning (CP-MAS) and dipolar dec oupled-magic angle spinning (DD-MAS) methods. This is possible because C-13 chemical shifts of the amino acid residues under consideration a re appreciably displaced, up to 8 ppm, depending upon particular confo rmations from several portions of membrane proteins such as the transm embrane alpha-helices, loops, N-or C-terminus, etc. as referred to the data accumulated to date of an appropriate model system. It is also p ossible to distinguish a region characterized by a variety of backbone motions with at least three different time scales from NMR data: rapi d motions with correlation times shorter than 10(-8) s, intermediate m otions with correlation times of 10(-4) to 10(-5) s, and slow motions with a time scale of 10(-2) s. In addition, we also explored a non-emp irical approach to reveal the three-dimensional structure of a smaller molecular system such as biologically active peptides as a messenger molecule in signal transduction, based on accurately determined approp riate sets of interatomic distances as determined by rotational echo d ouble resonance (REDOR). Examination of C-13 or N-15 chemical shifts b efore and after REDOR experiments proved to be an indispensable means to examine whether or not conformations of several kinds of C-13, N-15 -doubly labeled samples at different positions are not changed all the time. Here, we summarize some illustrative examples to this end, sele cted from our recent studies on [3-C-13]Ala-labeled bR and biologicall y active peptides such as enkephalins. (C) 1998 Elsevier Science B.V.