Taguchi J E, Heyes S J, Barford D, Johnson L N, Dobson C M
Oxford Centre for Molecular Sciences, University of Oxford, United Kingdom.
Biophys J. 1993 Feb;64(2):492-501. doi: 10.1016/s0006-3495(93)81392-4.
(31)P cross-polarization/magic angle sample spinning nuclear magnetic resonance spectra have been obtained for pyridoxal 5'-phosphate (PLP) bound to glycogen phosphorylase b (GPb) in two different crystalline forms, monoclinic and tetragonal. Analysis of the intensities of the spinning sidebands in the nuclear magnetic resonance spectra has enabled estimates of the principal values of the (31)P chemical shift tensors to be obtained. Differences between the two sets of values suggest differences in the environment of the phosphate moiety of the pyridoxal phosphate in the two crystalline forms. The tensor for the tetragonal crystalline form, T state GPb, is fully consistent with those found for dianionic phosphate groups in model compounds. The spectrum for the monoclinic crystalline form, R state GPb, although closer to that of dianionic than monoanionic model phosphate compounds, deviates significantly from that expected for a simple dianion or monoanion. This is likely to result from specific interactions between the PLP phosphate group and residues in its binding site in the protein. A possible explanation for the spectrum of the monoclinic crystals is that the shift tensor is averaged by a proton exchange process between different ionization states of the PLP associated with the presence of a sulfate ion bound in the vicinity of the PLP.
已获得与糖原磷酸化酶b（GPb）结合的磷酸吡哆醛（PLP）在两种不同晶体形式（单斜晶系和四方晶系）下的³¹P交叉极化/魔角旋转核磁共振谱。通过分析核磁共振谱中旋转边带的强度，得以获得³¹P化学位移张量主值的估计值。两组值之间的差异表明两种晶体形式中磷酸吡哆醛磷酸部分的环境存在差异。四方晶系晶体形式（T态GPb）的张量与模型化合物中双阴离子磷酸基团的张量完全一致。单斜晶系晶体形式（R态GPb）的谱图，虽然比单阴离子模型磷酸化合物的谱图更接近双阴离子的谱图，但与简单双阴离子或单阴离子预期的谱图有显著偏差。这可能是由于PLP磷酸基团与其在蛋白质中结合位点的残基之间的特定相互作用所致。单斜晶体谱图的一个可能解释是，由于在PLP附近结合的硫酸根离子的存在，与PLP相关的不同电离态之间的质子交换过程使位移张量平均化。
