Cloning And Expression Of The C-phycocyanin Gene From Nostoc Flagelliforme

Phycocyanin is a light-harvesting protein common to blue-green and red algae. Recent researches suggested phycocyanin also has lots of biology functions, such as scavenging free radicals, improving immunity, promoting cell proliferation, anti-tumor, anti-inflammatory, anti-radiation, anti-aging. Besides, it also has widely potential application in the fields of food, cosmetics, pharmaceutical and biotechnology. So it is very significant to clone and express phycocyanin.Using degenerate PCR primers,we cloned the C-phycocyanin gene from Nostoc flagelliforme (accession no. GU549478). The full-length DNA of C-phycocyanin was 1097 bp and consisted of two subunit,α- andβ-, with a 89 bp spacer. Theβ-subunit gene-coding region contains 519 bp and theα-subunit gene-coding region contains 489 bp.The estimated isoelectric point and molecular weight ofαsubunit protein were 5.90 and 17.457 kD, respectively. Correspondingly,βsubunit protein was 5.28 and 18.066 kD.The amino acid sequences showed considerable homology with the alpha and beta C-phycocyanin subunits from other species. Secondary structure prediction showed thatα,βsubunits of phycocyanin were major composed of alpha helixs and random coils construction elements. Their tertiary structures were also very similar. In both subunits proteins, the chromophores were attached by cysteinyl-thioether linkages atα84,β82 andβ153 positions, respectively.By inserting the alpha and beta gene into prokaryotic expressional vector pET28a to construct recombinant plasmid,the recombinant plasmid was transformed into E.coli strain BL21 and induced by IPTG to express. The results of SDS-PAGE electrophoresis indicated that the cpc gene had expressed in Ecoli.The molecular weight of expressed product of cpcαand cpcβwere about 17.5 kD and 18.0 kD, respectively.