Dioumaev A K, Brown L S, Needleman R, Lanyi J K
Department of Physiology & Biophysics, University of California, Irvine 92697, USA.
Biochemistry. 1998 Jul 14;37(28):9889-93. doi: 10.1021/bi980934o.
Photoisomerization of the all-trans-retinal of bacteriorhodopsin to 13-cis,15-anti initiates a sequence of thermal reactions in which relaxation of the polyene chain back to all-trans is coupled to various changes in the protein and the translocation of a proton across the membrane. We investigated the nature of this high-energy state in a genetically modified bacteriorhodopsin. When the electric charges of residues 85 and 96, the two aspartic acids critical for proton transport, are both changed to what they become after photoexcitation of the wild-type protein, i.e., neutral and anionic, respectively, the retinal assumes a thermally stable 13-cis,15-anti configuration. Thus, we have reversed cause and effect in the photocycle. It follows that when the 13-cis,15-anti isomeric state is produced by illumination, in the wild type it is unstable initially only because of conflicts with the retinal binding pocket. Later in the photocycle, the free energy gain is transferred from the chromophore to the protein. Before recovery of the initial state, it will come to be represented entirely by the free energy of the changed protonation states of aspartic acids 85 and 96.
细菌视紫红质的全反式视黄醛光异构化为13-顺式、15-反式会引发一系列热反应，其中多烯链弛豫回到全反式的过程与蛋白质的各种变化以及质子跨膜转运相耦合。我们研究了一种基因改造的细菌视紫红质中这种高能态的性质。当对质子转运至关重要的两个天冬氨酸残基85和96的电荷都变为野生型蛋白质光激发后所呈现的电荷状态，即分别变为中性和阴离子态时，视黄醛呈现出热稳定的13-顺式、15-反式构型。因此，我们在光循环中颠倒了因果关系。由此可知，当通过光照产生13-顺式、15-反式异构态时，在野生型中它最初不稳定仅仅是因为与视黄醛结合口袋存在冲突。在光循环后期，自由能增益从发色团转移到蛋白质上。在初始状态恢复之前，它将完全由天冬氨酸85和96质子化状态改变所带来的自由能来体现。
