Tosteson M T, Alvarez O, Hubbell W, Bieganski R M, Attenbach C, Caporales L H, Levy J J, Nutt R F, Rosenblatt M, Tosteson D C
Department of Cellular Molecular Physiology, Harvard Medical School, Boston, Massachusetts 02115.
Biophys J. 1990 Dec;58(6):1367-75. doi: 10.1016/S0006-3495(90)82483-8.
Melittin produces a voltage-dependent increase in the conductance of planar lipid bilayers. The conductance increases when the side of the membrane to which melittin has been added (cis-side) is made positive. This paper reports observations on the effect of modifying two positively charged amino acid residues within the NH2-terminal region of the molecule: lysine at position 7 (K7), and the NH2-terminal glycine (G1). We have synthesized melittin analogues in which K7 is replaced by asparagine (K7-N), G1 is blocked by a formyl group (G1-f), and in which both modifications of the parent compound were introduced (G1-f, K7-N). The time required to reach peak conductance during a constant voltage pulse was shorter in membranes exposed to the analogues than in membranes modified by melittin. The apparent number of monomers producing a conducting unit for [K7-N]-melittin and [G1-f]-melittin, eight, was found to be greater than the one for [G1-f], K7-N]-melittin and for melittin itself, four. The apparent gating charge per monomer was less for the analogues, 0.5-0.3 than for melittin, one. Essentially similar results were obtained with melittin analogues in which the charge on K7 or G1 or both was blocked by an uncharged N-linked spin label. These results show that the positive charges in the NH2-terminal region of melittin play a major but not exclusive role in the voltage gating of melittin channels in bilayers.
蜂毒肽可使平面脂质双分子层的电导产生电压依赖性增加。当添加蜂毒肽的膜侧（顺式侧）变为正电位时，电导增加。本文报道了对分子氨基末端区域内两个带正电荷的氨基酸残基进行修饰的效果观察：第7位的赖氨酸（K7）和氨基末端的甘氨酸（G1）。我们合成了蜂毒肽类似物，其中K7被天冬酰胺取代（K7-N），G1被甲酰基封闭（G1-f），并且引入了母体化合物的两种修饰（G1-f，K7-N）。在恒定电压脉冲期间达到峰值电导所需的时间，在暴露于类似物的膜中比在经蜂毒肽修饰的膜中更短。发现产生导电单位的[K7-N] - 蜂毒肽和[G1-f] - 蜂毒肽的单体表观数量为八个，大于[G1-f，K7-N] - 蜂毒肽和蜂毒肽本身的四个。类似物的每个单体的表观门控电荷比蜂毒肽少，分别为0.5 - 0.3和1。用K7或G1或两者的电荷被不带电荷的N-连接自旋标记封闭的蜂毒肽类似物获得了基本相似的结果。这些结果表明，蜂毒肽氨基末端区域的正电荷在双层中蜂毒肽通道的电压门控中起主要但非唯一的作用。
