The Diversity of Retinylidene Proteins in Microorganisma

盐盐菌（Halobacterium salinarium， H.salinarium）的紫红质（phoborhodopsin， PR）的吸收光谱表现出独特的特点：(1)与其他细菌的紫红质相比，其最大吸收峰有近100 nm的蓝移。(2)常温下表现为振动精细结构。我们最近的研究结果是：1.13-去甲基视网膜类似物在PR中重建了反向的疏光反应，而这种类似物对sr - i没有光化学（当然没有光行为）活性。PR中的发色团C6-C7键构象为s-反式，而PR中的发色团结合位点不像其他古细菌的红紫质那样受到限制。这是一项利用反式和顺式视网膜类似物进行的类似重建研究的结论，其中C6-C7构象被锁定在一个5元或7元环上。有趣的是，PR模拟色素是由6-s-顺式锁定（具有7元环）的视网膜重组而成的，该色素在视紫红质的发色团结合位点具有C5=C6-C7=C8的结构，靠近天然视网膜。然而，这种PR模拟物没有显示出振动的精细结构。盐碱地中PR的初级序列是最近才获得的，与法老钠杆菌和valismortis Haloarcula以及细菌视紫红质（bacteriorhodopsin）的相关色素具有密切的同源性（参见Zhang et al.Proc.Natl.Acad.Sci）。这一结果和上述结果证实了PR确实是古细菌红紫红质家族的成员，留下了古细菌红紫红质与动物视觉色素之间可能的系统发育关系的未解问题。

The absorption spectrum of phoborhodopsin (PR) of Halobacterium salinarium (H.salinarium) exhibits unique features : (1) The absorption maximum is nearly 100-nm blue shifted from those of other bacterial rhodopsins. (2) It shows vibrational fine structure at ambient temperatures. Our recent results are : .1.13-demethyl retinal analog reconstitutes inverted photophobic responses in PR,while this analog confers no photochemical (of course no photobehavioral) activity to SR-I.2. Conformation at C6-C7 bond of the chromophore has been confirmed to be s-trans in PR,whereas the chromophore binding site in PR is not so restricted like other archaebacterial rhodopsins. This has been the conclusion of an analog-reconstitution study using the both trans and cis retinal analogs in which C6-C7 conformation was locked with either a 5-membered or a 7-membered ring. Interestingly, PR analog pigment has been reconstituted from 6-s-cis locked (with 7-membered ring) retinal, which has a C5=C6-C7=C8 structure close to the native retinal at the chromophore binding site of visual rhodopsin. However, this PR analog showed no vibrational fine structure.3. The primary sequence of PR in H.salinarium has been obtained quite recently, showing close homology to the related pigments of Natronobacterium pharaonis and Haloarcula vallismortis as well as bacteriorhodopsin (see also Zhang et al.Proc.Natl.Acad.Sci.93,8230-8235,1996) This and the above results confirmed that PR is a genuine member of the family of archaebacterial rhodopsins, leaving the unsolved problem of possible phylogenic relationship between archaebacterial rhodopsins and animal visual pigments.