Gowen Joseph A, Markham Jeffrey C, Morrison Sara E, Cross Timothy A, Busath David D, Mapes Eric J, Schumaker Mark F
Zoology Department and Center for Neuroscience, Brigham Young University, Provo, Utah 84602, USA.
Biophys J. 2002 Aug;83(2):880-98. doi: 10.1016/S0006-3495(02)75215-6.
We present an extensive set of measurements of proton conduction through gramicidin A (gA), B (gB), and M (gM) homodimer channels which have 4, 3, or 0 Trp residues at each end of the channel, respectively. In gA we find a shoulder separating two domains of conductance increasing with concentration, confirming the results of Eisenman, G., B. Enos, J. Hagglund, and J. Sandblom. 1980. Ann. NY. Acad. Sci. 339:8-20. In gB, the shoulder is shifted by approximately 1/2 pH unit to higher H(+) concentrations and is very sharply defined. No shoulder appears in the gM data, but an associated transition from sublinear to superlinear I-V values occurs at a 100-fold higher [H(+)] in gM than in gA. The data in the low concentration domain are analyzed using a configuration space model of single-proton conduction, assuming that the difference in the proton potential of mean force (PMF) between gA and its analogs is constant, similar to the results of Anderson, D., R. B. Shirts, T. A. Cross, and D. D. Busath. 2001. Biophys. J. 81:1255-1264. Our results suggest that the average amplitudes of the calculated proton PMFs are nearly correct, but that the water reorientation barrier calculated for gA by molecular dynamics using the PM6 water model (Pomès, R., and B. Roux. 1997. Biophys. J. 72:246a) must be reduced in amplitude by 1.5 kcal/mol or more, and is not rate-limiting for gA.
我们展示了一系列广泛的测量结果，这些测量是关于质子通过短杆菌肽A（gA）、B（gB）和M（gM）同型二聚体通道的传导情况，这些通道在通道两端分别有4个、3个或0个色氨酸残基。在gA中，我们发现一个拐点将两个随浓度增加的电导区域分隔开，这证实了艾森曼（G. Eisenman）、B. 伊诺斯（B. Enos）、J. 哈格隆德（J. Hagglund）和J. 桑德布洛姆（J. Sandblom）的研究结果。1980年，《纽约科学院学报》339卷：8 - 20页。在gB中，该拐点向更高的H⁺浓度方向移动了约1/2个pH单位，并且定义非常清晰。gM的数据中没有出现拐点，但在gM中，从亚线性到超线性I - V值的相关转变发生时的[H⁺]浓度比gA中的高100倍。使用单质子传导的构型空间模型对低浓度区域的数据进行了分析，假设gA与其类似物之间的平均力质子势（PMF）差异是恒定的，这与安德森（D. Anderson）、R. B. 希茨（R. B. Shirts）、T. A. 克罗斯（T. A. Cross）和D. D. 布萨特（D. D. Busath）的研究结果相似。2001年，《生物物理学杂志》81卷：1255 - 1264页。我们的结果表明，计算得到的质子PMF的平均幅度几乎是正确的，但使用PM6水模型通过分子动力学为gA计算的水重排势垒（波梅斯（R. Pomès）和B. 鲁克斯（B. Roux），1997年，《生物物理学杂志》72卷：246a）的幅度必须降低1.5千卡/摩尔或更多，并且它对gA来说不是限速因素。
