Cyc2 is the key protein in the outer membrane of Acidithiobacillus ferrooxidans that mediates electron transfer between extracellular inorganic iron and the intracellular central metabolism. This cytochrome c is specific for iron and interacts with periplasmic proteins to complete a reversible electron transport chain. A structure of Cyc2 has not yet been characterized experimentally. Here we describe a structural model of Cyc2, and associated proteins, to highlight a plausible mechanism for the ferrous iron electron transfer chain. A comparative modeling protocol specific for trans membrane beta barrel (TMBB) proteins in acidophilic conditions (pH ~ 2) was applied to the primary sequence of Cyc2. The proposed structure has three main regimes: Extracellular loops exposed to low-pH conditions, a TMBB, and an N-terminal cytochrome-like region within the periplasmic space. The Cyc2 model was further refined by identifying likely iron and heme docking sites. This represents the first computational model of Cyc2 that accounts for the membrane microenvironment and the acidity in the extracellular matrix. This approach can be used to model other TMBBs which can be critical for chemolithotrophic microbial growth.

中文翻译：

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计算结构预测为氧化亚铁硫杆菌的外膜蛋白 Cyc2 的电子转移提供了一种合理的机制

Cyc2是氧化亚铁硫杆菌外膜的关键蛋白介导细胞外无机铁和细胞内中枢代谢之间的电子转移。这种细胞色素 c 对铁具有特异性，并与周质蛋白相互作用以完成可逆的电子传递链。Cyc2 的结构尚未通过实验表征。在这里，我们描述了 Cyc2 和相关蛋白质的结构模型，以突出亚铁电子转移链的合理机制。在嗜酸条件 (pH ~ 2) 下对跨膜 β 桶 (TMBB) 蛋白特异的比较建模协议应用于 Cyc2 的一级序列。所提出的结构具有三个主要方案：暴露于低 pH 条件下的细胞外环、TMBB 和周质空间内的 N 端细胞色素样区域。通过识别可能的铁和血红素对接位点，Cyc2 模型得到了进一步完善。这代表了 Cyc2 的第一个计算模型，该模型解释了膜微环境和细胞外基质中的酸度。这种方法可用于模拟其他对化能营养微生物生长至关重要的 TMBB。