Cloning of apcE gene from Arthrospira platensis FACHB314 and its function in heterologous expression.

The phycobilisomes attached to the outer side of the thylakoid membrane absorb and transmit light energy in cyanobacteria and red algae. They consist of phycobiliproteins and linker polypeptides. LCM involved in the attachment of the phycobilisomes to the membrane is called core–membrane linker polypeptide. This study aimed to clone the apcE gene encoding the core–membrane linker polypeptide ApcE from Arthrospira platensis FACHB314. Then, the apcE gene was expressed with phycocyanobilin synthesis–related elements in Escherichia coli. The fluorescence emission spectra showed that purified ApcE was fluorescing (λmax = 670 nm), indicating that ApcE could bind with phycocyanobilin in low yield in an autocatalytic reaction. The Cys201, Cys419, Cys616, and Cys644 of the polypeptide were mutated to investigate the binding sites of ApcE with phycocyanobilin. The fluorescence peak of mutant strain E.coli HPApcE201 almost did not exist, implying that Cys201was the binding site of ApcE. The ApcE and allophycocyanin (APC) or phycocyanins (PC) were co-expressed in E. coli separately to investigate the role of ApcE in the fluorescence activity of phycobiliproteins. The mass spectrometry results showed that high–molecular weight protein polymers of ApcE and APC or of ApcE and PC might exist. The fluorescence emission spectra showed that the characteristic fluorescence peak of APC and PC was higher and the wavelength range of fluorescence peak was larger with ApcE expression. [ABSTRACT FROM AUTHOR]