Hicks David B, Liu Jun, Fujisawa Makoto, Krulwich Terry A
Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY 10029, USA.
Biochim Biophys Acta. 2010 Aug;1797(8):1362-77. doi: 10.1016/j.bbabio.2010.02.028. Epub 2010 Mar 1.
This review focuses on the ATP synthases of alkaliphilic bacteria and, in particular, those that successfully overcome the bioenergetic challenges of achieving robust H+-coupled ATP synthesis at external pH values>10. At such pH values the protonmotive force, which is posited to provide the energetic driving force for ATP synthesis, is too low to account for the ATP synthesis observed. The protonmotive force is lowered at a very high pH by the need to maintain a cytoplasmic pH well below the pH outside, which results in an energetically adverse pH gradient. Several anticipated solutions to this bioenergetic conundrum have been ruled out. Although the transmembrane sodium motive force is high under alkaline conditions, respiratory alkaliphilic bacteria do not use Na+- instead of H+-coupled ATP synthases. Nor do they offset the adverse pH gradient with a compensatory increase in the transmembrane electrical potential component of the protonmotive force. Moreover, studies of ATP synthase rotors indicate that alkaliphiles cannot fully resolve the energetic problem by using an ATP synthase with a large number of c-subunits in the synthase rotor ring. Increased attention now focuses on delocalized gradients near the membrane surface and H+ transfers to ATP synthases via membrane-associated microcircuits between the H+ pumping complexes and synthases. Microcircuits likely depend upon proximity of pumps and synthases, specific membrane properties and specific adaptations of the participating enzyme complexes. ATP synthesis in alkaliphiles depends upon alkaliphile-specific adaptations of the ATP synthase and there is also evidence for alkaliphile-specific adaptations of respiratory chain components.
本综述聚焦于嗜碱细菌的ATP合酶,尤其是那些能够成功克服生物能量挑战,在外部pH值>10的条件下实现强大的H⁺偶联ATP合成的ATP合酶。在这样的pH值下,据推测为ATP合成提供能量驱动力的质子动力势过低,无法解释所观察到的ATP合成。在非常高的pH值下,由于需要将细胞质pH维持在远低于外部pH的水平,质子动力势会降低,这会导致能量上不利的pH梯度。针对这一生物能量难题的几种预期解决方案已被排除。尽管在碱性条件下跨膜钠动力势很高,但呼吸嗜碱细菌并不使用Na⁺偶联而非H⁺偶联的ATP合酶。它们也不会通过质子动力势跨膜电势成分的补偿性增加来抵消不利的pH梯度。此外,对ATP合酶转子的研究表明,嗜碱菌无法通过使用在合酶转子环中具有大量c亚基的ATP合酶来完全解决能量问题。现在越来越多的注意力集中在膜表面附近的离域梯度以及H⁺通过H⁺泵复合物与合酶之间的膜相关微电路转移到ATP合酶上。微电路可能取决于泵与合酶的接近程度、特定的膜特性以及参与酶复合物的特定适应性。嗜碱菌中的ATP合成取决于ATP合酶的嗜碱菌特异性适应性,也有证据表明呼吸链成分存在嗜碱菌特异性适应性。
Biochim Biophys Acta. 2010-8
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