Marsh Derek
Max-Planck-Institut für biophysikalische Chemie, Abt. Spektroskopie, 37070 Göttingen, Germany.
J Magn Reson. 2006 Jun;180(2):305-10. doi: 10.1016/j.jmr.2006.02.007. Epub 2006 Feb 28.
The orientation of alpha-helices or beta-strands, e.g., in membranes, can be determined from EPR order parameters of (2,2,6,6-tetramethyl-piperidine-1-oxy-4-amino-4-carboxylic acid) TOAC amino-acid spin labels incorporated in the polypeptide backbone. This requires knowledge of the inclination of the nitroxide axes, relative to the alpha-helix or beta-strand axis. Crystal structures of TOAC-containing peptides are used to derive the spin-label orientation relative to refined alpha-poly-l-alanine and beta-poly-l-alanine structures. The spin-label z-axes of the two mirror-image TOAC twist-boat conformers are inclined at 13+/-2 degrees and 65+/-3 degrees , respectively, to the alpha-helix axis, or at 25+/-3 degrees and 32+/-3 degrees to the beta-strand axis.
例如，在膜中，α-螺旋或β-链的取向可以通过掺入多肽主链中的（2,2,6,6-四甲基哌啶-1-氧基-4-氨基-4-羧酸）TOAC氨基酸自旋标记的电子顺磁共振序参量来确定。这需要了解氮氧化物轴相对于α-螺旋或β-链轴的倾斜度。含TOAC的肽的晶体结构用于推导相对于精制的α-聚-L-丙氨酸和β-聚-L-丙氨酸结构的自旋标记取向。两个镜像TOAC扭曲船构象体的自旋标记z轴分别相对于α-螺旋轴倾斜13±2度和65±3度，或者相对于β-链轴倾斜25±3度和32±3度。
