CSIR-Institute of Microbial Technology, Chandigarh, India.
Department of Biotechnology, Panjab University, Chandigarh, India.
Front Cell Infect Microbiol. 2022 Feb 10;11:796727. doi: 10.3389/fcimb.2021.796727. eCollection 2021.
() produces an unconventional flavohemoglobin (FHb) that carries a FAD-binding site similar to D-lactate dehydrogenases (D-LDH) and oxidizes D-lactate into pyruvate. The molecular mechanism by which FHb functions in remains unknown. We discovered that the D-LDH-type FAD-binding site in FHb overlaps with another FAD-binding motif similar to thioredoxin reductases and reduces DTNB in the presence of NADPH similar to trxB of . These results suggested that FHb is functioning as a disulfide oxidoreductase. Interestingly, D-lactate created a conformational change in FHb and attenuated its ability to oxidize NADPH. Mass spectroscopy demonstrated that FHb reduces des-inositol mycothiol in the presence of D-lactate unlike NADPH, indicating that D-lactate changes the specificity of FHb from di-thiol to di-mycothiol. When carrying deletion in the II gene (encoding a homolog of FHb) was complemented with the gene of , it exhibited four- to fivefold reductions in lipid peroxidation and significant enhancement in the cell survival under oxidative stress. These results were corroborated by reduced lipid peroxidation and enhanced cell survival of wild-type after overexpression of the gene of . Since D-lactate is a by-product of lipid peroxidation and FHb is a membrane-associated protein, D-lactate-mediated reduction of mycothiol disulfide by FHb may uniquely equip to relieve the toxicity of D-lactate accumulation and protect the cell from oxidative damage, simultaneously balancing the redox environment under oxidative stress that may be vital for the pathogenesis of .
() 产生一种非常规的黄素血红蛋白 (FHb)，它携带一个类似于 D-乳酸脱氢酶 (D-LDH) 的 FAD 结合位点，并将 D-乳酸氧化为丙酮酸。FHb 在 中发挥作用的分子机制尚不清楚。我们发现，FHb 中的 D-LDH 型 FAD 结合位点与另一个类似于硫氧还蛋白还原酶的 FAD 结合模体重叠，并在 NADPH 的存在下类似于 中的 trxB 还原 DTNB。这些结果表明 FHb 充当二硫键氧化还原酶。有趣的是，D-乳酸在 FHb 中引起构象变化，并减弱其氧化 NADPH 的能力。质谱分析表明，与 NADPH 不同，D-乳酸在存在时使 FHb 还原去肌醇麦硫因，表明 D-乳酸改变了 FHb 的特异性，从二硫键变为二麦硫因。当 中缺失编码 FHb 同源物的 II 基因时，用 基因进行互补，在氧化应激下，其脂质过氧化减少了四到五倍，细胞存活率显著提高。这些结果得到了野生型 的脂质过氧化减少和细胞存活率提高的验证，该野生型在过表达 基因后。由于 D-乳酸是脂质过氧化的副产物，而 FHb 是一种膜相关蛋白，因此 D-乳酸通过 FHb 还原麦硫因二硫键可能独特地使 能够缓解 D-乳酸积累的毒性并保护细胞免受氧化损伤，同时平衡氧化应激下的氧化还原环境，这对于 的发病机制可能至关重要。
