Blanck A, Oesterhelt D, Ferrando E, Schegk E S, Lottspeich F
Max-Planck-Institut für Biochemie, Martinsried, FRG.
EMBO J. 1989 Dec 20;8(13):3963-71. doi: 10.1002/j.1460-2075.1989.tb08579.x.
The gene coding for sensory rhodopsin I (SR-I) has been identified in a restriction fragment of genomic DNA from the Halobacterium halobium strain L33. Of the 1014 nucleotides whose sequence was determined, 720 belong to the structural gene of SR-I. In the 5' non-coding region two putative promoter elements and a ribosomal binding site have been identified. The 3' flanking region bears a potential terminator structure. The SR-I protein moiety carries no signal peptide and is not processed at its N terminus. The C terminus, however, lacks the last aspartic acid residue encoded by the gene. Analysis of the primary structure of SR-I reveals no consistent homology with the eukaryotic photoreceptor rhodopsin, but 14% homology with the halobacterial ion pumps, bacteriorhodopsin (BR) and halorhodopsin (HR). Residues conserved in all three proteins are discussed with respect to their contribution to secondary structure, retinal binding and ion translocation. The aspartic acid residue which mediates in BR the reprotonation of the Schiff base (D96) is replaced in SR-I by a tyrosine (Y87). This amino acid replacement is proposed to be of crucial importance in the evolution of the slow-cycling photosensing pigment SR-I.
已在嗜盐栖热菌L33菌株基因组DNA的一个限制性片段中鉴定出编码感官视紫红质I（SR-I）的基因。在已确定序列的1014个核苷酸中，720个属于SR-I的结构基因。在5'非编码区已鉴定出两个假定的启动子元件和一个核糖体结合位点。3'侧翼区具有潜在的终止子结构。SR-I蛋白部分没有信号肽，其N端也未进行加工。然而，C端缺少该基因编码的最后一个天冬氨酸残基。对SR-I一级结构的分析表明，它与真核生物光感受器视紫红质没有一致的同源性，但与嗜盐菌离子泵细菌视紫红质（BR）和嗜盐视紫红质（HR）有14%的同源性。讨论了在这三种蛋白质中保守的残基对二级结构、视黄醛结合和离子转运的贡献。在BR中介导席夫碱再质子化的天冬氨酸残基（D96）在SR-I中被酪氨酸（Y87）取代。这种氨基酸取代被认为在慢循环光传感色素SR-I的进化中至关重要。
