Streptococcal pyruvate oxidase (SpxB) is a hydrogen peroxide-generating enzyme and plays a critical role in Streptococcus sanguinis interspecies interactions, but less is known about its biochemistry. We examined SpxB subcellular localization using protein fractionation and microscopy and found SpxB to be primarily cytoplasmic, but a small portion is also membrane associated. Potential post-translational modifications of SpxB were determined using coimmunoprecipitation and mass spectrometry. Two mutant strains were constructed to further validate the presence of predicted site-specific post-translational modifications. These site mutated SpxB proteins exhibited reduced solubility in vivo, which likely contributes to the observed phenotypic changes in colony morphology, bacterial growth, and H₂O₂ production. Overall, our data suggest that SpxB post-translational modifications likely play a major role to regulate SpxB function in S. sanguinis.

中文翻译：

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Streptococcus sanguinis SpxB 的翻译后修饰影响蛋白质溶解度和 H2O2 产生

链球菌丙酮酸氧化酶 (SpxB) 是一种产生过氧化氢的酶，在血链球菌种间相互作用中起关键作用，但对其生物化学知之甚少。我们使用蛋白质分级和显微镜检查了 SpxB 亚细胞定位，发现 SpxB 主要是细胞质的，但一小部分也与膜相关。使用共免疫沉淀和质谱法确定了 SpxB 的潜在翻译后修饰。构建了两个突变菌株以进一步验证预测的位点特异性翻译后修饰的存在。这些位点突变的 SpxB 蛋白在体内表现出降低的溶解度，这可能有助于观察到的菌落形态、细菌生长和 H _{2的表型变化}O ₂生产。总体而言，我们的数据表明，SpxB 翻译后修饰可能在调节S. sanguinis中的 SpxB 功能中起主要作用。