Wang Z Y, Shimonaga M, Muraoka Y, Kobayashi M, Nozawa T
Department of Biomolecular Engineering, Faculty of Engineering, Center for Interdisciplinary Research, Tohoku University, Sendai, Japan.
Eur J Biochem. 2001 Jun;268(12):3375-82. doi: 10.1046/j.1432-1327.2001.02234.x.
An additional component in the purified core light-harvesting complex (LH1) from wild-type purple photosynthetic bacterium Rhodospirillum rubrum has been identified as an oxidized species of alpha-polypeptide by MALDI-TOF mass spectrometry. This component appears as a slightly earlier-eluting peak in the RP-HPLC chromatogram compared with the authentic alpha-polypeptide. The oxidation site has been determined to be the N-terminal methionine residue by high-resolution NMR spectroscopy, where the methionine is oxidized to methionine sulfoxide in a diastereoisomeric form. Interconversion between the oxidized and authentic alpha-polypeptides has been confirmed by selective oxidation and reduction. The oxidative modification of methionine is shown to have discernible effects on the ability to form B820 subunit with beta-polypeptide and bacteriochlorophyll a, and on the stability of the reconstituted B820 subunit. Both the ability and the stability for the samples using the oxidized alpha-polypeptide are moderately reduced, indicating that the oxidation-induced conformational change in the N-terminal domain of alpha-polypeptide may affect the pigment-binding environment through a long-range interaction. The MALDI-TOF mass results also reveal that the N-terminus of alpha-polypeptide is formylated and no phosphorylation has occurred in this polypeptide.
通过基质辅助激光解吸电离飞行时间质谱（MALDI-TOF），已确定来自野生型紫色光合细菌红螺菌（Rhodospirillum rubrum）的纯化核心捕光复合物（LH1）中的一种额外成分是α-多肽的氧化形式。与真实的α-多肽相比，该成分在反相高效液相色谱（RP-HPLC）色谱图中表现为洗脱稍早的峰。通过高分辨率核磁共振光谱确定氧化位点为N端甲硫氨酸残基，其中甲硫氨酸被氧化为非对映异构体形式的甲硫氨酸亚砜。通过选择性氧化和还原证实了氧化型和真实α-多肽之间的相互转化。结果表明，甲硫氨酸的氧化修饰对与β-多肽和细菌叶绿素a形成B820亚基的能力以及重组B820亚基的稳定性有明显影响。使用氧化型α-多肽的样品的能力和稳定性均适度降低，这表明α-多肽N端结构域中氧化诱导的构象变化可能通过长程相互作用影响色素结合环境。MALDI-TOF质谱结果还表明，α-多肽的N端被甲酰化，且该多肽未发生磷酸化。
