J_+Experiment+07_+v+F10 - 7-1Experiment 1997 an open...

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Unformatted text preview: 7-1Experiment 7THEEXPRESSIONOFANORF FROMACYANOBACTERIUMINANE. COLIHOSTIntroductionIn 1997, an open reading frame (ORF) was found at locus slr1784in cyanobacterium Synechocystis PCC 6803 upon completion of its genomic sequence. Due to sequence similarities with other proteins listed in the databanks, the ORF was shown to be similar to biliverdin reductase from mammals, and was annotated as a putative biliverdin reductase (BVR). The ORF encodes a 328 amino acid polypeptide which is 23% identical to mammalian biliverdin IXαreductase. A multiple sequence alignment of the protein encoded by locus slr1784with BVR sequences from rat and human is shown in Figure 7.1.RatBVRHumanBVRSlr1784RatBVRHumanBVRSlr1784RatBVRHumanBVRSlr1784RatBVRHumanBVRSlr1784RatBVRHumanBVRSlr1784RatBVRHumanBVRSlr1784RatBVRHumanBVRSlr1784RatBVRHumanBVRSlr17844413977788212121125155156168195196211234235254263264295295296328--MDAEPKRKFGVVVVGVGRAGSVRLRDLKDPR-SAAFLNLIG--MNTEPERKFGVVVVGVGRAGSVRMRDLRNPHPSSAFLNLIGMSENFAVATPVRVGIVGTGYAAQRRAEVFRGDRRS----QLVSFVSRRE------LGSLDEVRQISLEDALRSQEIDVAYICSESSFVSRRE------LGSIDGVQQISLEDALSSQEVEVAYICSESSFWGNSEANTAKFADTFGVRPQQSWQALINDPEIDLVLIATINQSHEDYIRQFLQAGKHVLVEYPMTLSFAAAQELWELAAQKGRVLSHEDYIRQFLNAGKHVLVEYPMTLSLAAAQELWELAEQKGKVLLHGAIAEAALQAGKHVVLEYPLALTYAMGKKLQQLAREKGKLLHEEHVELLMEEFEFLRREV--LGKELL-KGSLRFTASP-----HEEHVELLMEEFAFLKKEV--VGKDLL-KGSLLFTAGP-----HVEHIELLGGVHQAIRQNLGKIGEVFYARYSTIMGQNPAPQRW-LEEERFGFPAFSGISRLTWLVSLFGELSLISA--TLEERKED-LEEERFGFPAFSGISRLTWLVSLFGELSLVSA--TLEERKEDTYHHQQFGFPLVAALSRISRFTDLFGTVQQVDAQCRFWDQPNPQYMK---MTVQLETQNKGLLSWIEEKGPGLKRN-RYVNFQFTSQYMK---MTVCLETEKKSPLSWIEEKGPGLKRN-RYLSFHFKSEYFRACLATAYLQFNNGLKAEVIYGKGEVFHQNERIFTLHGDRGSL--------------EEVPSVGVNKNIFLKDQDIFVQKLLDGSL--------------ENVPNVGVNKNIFLKDQNIFVQKLLGGTLIFVGETGRLIQGQTETEITVGSRRGLFRQDTEAVLDYL--QVSAEDLAAEKKRIMHCLGLASDIQKLCHQKK--QFSEKELAAEKKRILHCLGLAEEIQKYCCSRK---TTGKPLYVDLEASLYALEVADLCAQACGYKVENFigure 7.1Multiple Sequence Alignment of Cyanobacterial and Mammalian Biliverdin Reductases.BVR catalyzes the reduction of biliverdin IXα (BV) to bilirubin (BR) comprising the final step of heme catabolism in mammals and some species of fish as seen in Figure 7.2. Hence, finding an enzyme of typically vertebrate function in a cyanobacterium is a surprise (which also underscores the importance of the genome projects). This leads to the obvious question, what is the function, if any, of the protein encoded by the ORF of locus slr1784(iethe putative BVR) in this prokaryotic photosynthetic organism? Cyanobacteria certainly contain hemes, but if the putative BVR does not function as a BVR enzyme in the cyanobacterium, then what is its function? The functions of many proteins are derived by the divergence of genes through evolutionary processes. If the cyanobacterial ORF and the mammalian BVR gene are evolutionarily related, then the mammalian gene likely diverged from the earlier prokaryotic gene with altered substrate specificity.7-2Figure 7.2 Heme catabolism to biliverdin, and reduction of biliverdin to bilirubin. Heme catabolism to biliverdin, and reduction of biliverdin to bilirubin....
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J_+Experiment+07_+v+F10 - 7-1Experiment 1997 an open...

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