Tyrosine, phenylalanine, and disulfide contributions to the circular dichroism of proteins: Circular dichroism spectra of wild-type and mutant bovine pancreatic trypsin inhibitor
Tyrosine, phenylalanine, and disulfide contributions to the circular dichroism of proteins: Circular dichroism spectra of wild-type and mutant bovine pancreatic trypsin inhibitor
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DOI：
10.1021/bi990516z
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发表时间：
1999-08-17
期刊：
影响因子：
2.9
通讯作者：
Woody, RW
中科院分区：
文献类型：
--
作者：
Sreerama, N;Manning, MC;Woody, RW
为了扩展计算蛋白质圆二色性（CD）光谱的能力，改进了酪氨酸和苯丙氨酸侧链最低能量激发态的描述。考虑了每个侧链发色团的四个跃迁（L-b，L-a，B-b和B-a），并从代表各个基团的模型的CNDO/S计算中获得跃迁的电荷。还包括键中点处的单极电荷（对应于L-B带中的最大跃迁电荷密度）和代表与L-a跃迁的B跃迁的电子振动耦合的负电荷。在非来源依赖矩阵方法的框架下，将芳香族跃迁与肽跃迁（n pi*，pi（0）pi* n 'pi *，pi+pi*）和二硫键跃迁（n（1）sigma*，n（4）sigma*）相结合，计算了牛胰蛋白酶抑制剂（BPTI）不同晶型和Y -> L，F -> L突变体的圆二色光谱.突变体的结构通过在野生型晶体结构中用亮氨酸替换适当的酪氨酸或苯丙氨酸残基而获得。对能量最小化结构进行了CD计算。计算的BPTI的II型晶体结构的CD光谱显示与实验的最佳一致性。在远紫外，计算和实验CD光谱同意不同程度的野生型和突变体BPTI。其中Y 4L、Y10 L、Y23 L和F45 L的CD谱计算值与实验值吻合较好，而Y21 L和F22 L这两个与芳香基团相互作用最多的残基的CD谱计算值与实验值吻合较差。在近紫外，预测的野生型和突变体BPTI的负带的强度比实验观察到的要小得多。
Improved descriptions of the lowest energy excited states of tyrosine and phenylalanine side chains have been developed in order to extend the capabilities of calculating the circular dichroism (CD) spectra of proteins. Four transitions (L-b, L-a, B-b, and B-a) for each of the side-chain chromophores were considered, and the transition monopole charges were obtained from a CNDO/S calculation on models representing the individual groups. Monopole charges at midpoints of the bonds, corresponding to the maximum transition charge densities in the L-b band, and monopole charges representing the vibronic coupling with the B transitions for the L-a transition were also included. The aromatic transitions were combined with the peptide transitions (n pi*, pi(0)pi* n'pi*, and pi+pi*) and disulfide transitions (n(1)sigma* and n(4)sigma*) in the framework of the origin-independent matrix method to compute the CD spectra of different crystal forms and Y --> L and F --> L mutants of bovine pancreatic trypsin inhibitor (BPTI). The structures of the mutants were obtained by replacing the appropriate tyrosine or phenylalanine residue by leucine in the wild-type crystal structure. The CD calculations were performed on the energy-minimized structures. The CD spectrum calculated for the form II crystal structure of BPTI showed the best agreement with experiment. In the far UV, the calculated and experimental CD spectra agree to various extents for the wild-type and mutant BPTI. Among the mutants, the calculated CD spectra of Y4L, Y10L, Y23L, and F45L showed reasonable a,agreement with experiment, while those of Y21L and F22L, the two residues interacting with most aromatic groups, showed poor agreement. In the near UV, the negative bands predicted for the wild-type and mutant BPTI have much less intensity than observed experimentally.