Furini Simone, Domene Carmen
Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford OX13QZ, United Kingdom.
Proc Natl Acad Sci U S A. 2009 Sep 22;106(38):16074-7. doi: 10.1073/pnas.0903226106. Epub 2009 Sep 4.
Potassium channels can conduct passively K+ ions with rates of up to approximately 10(8) ions per second at physiological conditions, and they are selective to these species by a factor of 10(4) over Na+ ions. Ion conduction has been proposed to involve transitions between 2 main states, with 2 or 3 K+ ions occupying the selectivity filter separated by an intervening water molecule. The largest free energy barrier of such a process was reported to be of the order of 2-3 kcal mol(-1). Here, we present an alternative mechanism for conduction of K+ in potassium channels where site vacancies are involved, and we propose that coexistence of several ion permeation mechanisms is energetically possible. Conduction can be described as a more anarchic phenomenon than previously characterized by the concerted translocations of K+-water-K+.
钾离子通道在生理条件下能够以高达每秒约10⁸个离子的速率被动传导钾离子，并且它们对这些离子的选择性比对钠离子高10⁴倍。离子传导被认为涉及两个主要状态之间的转变，其中2个或3个钾离子占据选择性过滤器，中间隔着一个水分子。据报道，这样一个过程的最大自由能垒约为2 - 3千卡/摩尔。在这里，我们提出了一种钾离子通道中钾离子传导的替代机制，其中涉及位点空位，并且我们提出几种离子渗透机制共存在能量上是可能的。传导可以被描述为一种比以前由K⁺-水-K⁺的协同转运所描述的更为无序的现象。
