OccK channels from Pseudomonas aeruginosa exhibit diverse single-channel electrical signatures but conserved anion selectivity.
OccK channels from Pseudomonas aeruginosa exhibit diverse single-channel electrical signatures but conserved anion selectivity.
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DOI：
10.1021/bi300066w
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发表时间：
2012-03-20
期刊：
影响因子：
2.9
通讯作者：
Movileanu L
中科院分区：
文献类型：
--
作者：
Liu J;Eren E;Vijayaraghavan J;Cheneke BR;Indic M;van den Berg B;Movileanu L
铜绿假单胞菌是一种革兰氏阴性细菌，其利用底物特异性外膜（OM）蛋白来摄取细胞生长和功能中使用的小的水溶性营养物。在本文中，我们提出了第一次全面的单通道检查的OM羧酸通道K（OccK）亚家族的七个成员。最近对OccK蛋白的生物化学、功能和结构表征揭示了它们的共同特征，例如具有肾形跨膜孔的密切相关的单体18链β-桶构象和通道腔内存在基本梯状结构。在这里，我们报告说，OccK蛋白质表现出相当不同的单位电导值，在一个比早期的预期，其中包括低（~40-100 pS）和中等（~100-380 pS）电导更广泛的范围。这些蛋白质表现出不同的单通道动力学的电流门控转换，揭示了一个（OccK 3），两个（OccK 4，OccK 5和OccK 6）和三个（OccK 1，OccK 2和OccK 7）-开放的子状态动力学与功能不同的构象。有趣的是，我们发现阴离子选择性是OccK亚家族成员之间的保守特征，证实了它们的中央收缩内存在带正电荷的残基的净池。此外，这些结果与这些蛋白质通道对带负电荷的含羧酸盐底物的特异性和选择性增加雅阁。我们的研究结果可能会点燃未来的功能检查和全原子计算研究，以揭示小分子穿过底物特异性β-桶OM蛋白内腔的机制。
Pseudomonas aeruginosa is a Gram-negative bacterium that utilizes substrate-specific outer membrane (OM) proteins for the uptake of small, water-soluble nutrients employed in the growth and function of the cell. In this paper, we present for the first time a comprehensive single-channel examination of seven members of the OM carboxylate channel K (OccK) subfamily. Recent biochemical, functional and structural characterization of the OccK proteins revealed their common features, such as a closely related, monomeric, 18-stranded β-barrel conformation with a kidney-shaped transmembrane pore and the presence of a basic ladder within the channel lumen. Here, we report that the OccK proteins exhibited fairly distinct unitary conductance values, in a much broader range than earlier expectations, which includes low (~40–100 pS) and medium (~100–380 pS) conductance. These proteins showed diverse single-channel dynamics of current gating transitions, revealing one (OccK3)-, two (OccK4, OccK5 and OccK6)- and three (OccK1, OccK2 and OccK7)-open sub-state kinetics with functionally distinct conformations. Interestingly, we discovered that anion selectivity is a conserved trait among the members of the OccK subfamily, confirming the presence of a net pool of positively charged residues within their central constriction. Moreover, these results are in accord with an increased specificity and selectivity of these protein channels for negatively charged, carboxylate-containing substrates. Our findings might ignite future functional examinations and full-atomistic computational studies for unraveling a mechanistic understanding of the passage of small molecules across the lumen of substrate-specific, β-barrel OM proteins.