The Diversity of Retinylidene Proteins in Microorganisma

盐生盐杆菌的视紫红质(PR)的吸收光谱表现出独特的特征：(1)其最大吸收峰较其他细菌的视紫红质有近100 nm的蓝移；(2)在常温下表现出振动精细结构。我们最近的结果是：1.13-去甲基视网膜类似物在PR中重建了反向的畏光反应，而该类似物没有给予SR-I任何光化学(当然没有光行为)活性。发色团C6-C7键的构象已被证实为PR中的S反式，而PR中的发色团结合部位不像其他考古细菌视紫红质那样受到限制。这是一项使用反式和顺式视网膜类似物的模拟重建研究的结论，在该研究中，C6-C7构象被5元环或7元环锁定。有趣的是，PR类似色素是由6-S-顺式锁定(具有7元环)的视网膜重组的，其结构为C5=C6-C7=C8，在视紫红质的生色团结合部位接近天然视网膜。然而，这种PR类似物没有表现出振动精细结构。盐酸菌中PR的一级序列是最近获得的，它与细菌视紫红质和法老纳氏杆菌的相关色素以及细菌视紫红质的同源性很高(另见Zhang等人，Proc.Natl.Academy，93,8230-8235,1996)。以上结果证实了PR是考古细菌视紫质蛋白家族中的一个真正的成员，留下了考古菌视紫红质与动物视紫红质之间可能的系统发育关系的悬而未决的问题。

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.