The Relations Between Structure And Function Of The Phycobiliprotein Which Can Autoassembly With Phycobilin

Based on their absorption spectral properties, phycobiliproteins have been assigned to four classes: phycocyanin (PC), phycoerythrin (PE), allophycocyanin (APC) and phycoerythrocyanin (PEC), in which the latter is primarily found in certain filamentous, heterocyst-forming cyanobacteria. Cyanobacterial phytochrome and allophycocyanin are all the phycobiliprotein that can autoassembly with PCB. Cyanobacterial phytochrome AphA has highly reversibly photochromic activity. With low molecular weight and simple structure, AphA has predominance in studies on dynamic states of reversible photochromism and photoswitch design. To study the relationship between the structure of aphA and its function, mutants AphA(26-320), AphA(27-320), AphA(28-320), AphA(29-320) and AphA(32-320) were constructed. The experimental results indicated that only the AphA(26-320) has the function of autoassemblying with PCB.This stated that the lyase domain of AphA existing in AphA(26-320)。Any further delation mutation would disable the lyase function. From our laboratory's study, we speculated that the Cys-196 is the chromophore-binding site in ApcE(1-240). Via homologuous align the motif around S158 in Apce(1-240) may be the chromophore-binding site ,like in CpcB and ApcB. If the S158 was mutated C, the resulting C158 would be band by PCB. For proving these, we used site-directed mutation to generate two mutants, apcE(1-240)(C196I) and apcE(1-240)(C196I,S158C). The overexpressed proteins were direct used to reconstitution with pigment PCB in vitro. The experimental results indicated that the Cys-196 is the chromophore-binding site in ApcE(1-240) and the Ser in the homologous region which of the ApcE(1-240), CpcB and ApcB mutated Cys have not the function of autoassemblying with PCB. For finding the allophycocyanin that have smaller molecular weight and better water-solubility than the ApcE(1-240) and have the function of autoassemblying with PCB all the same, we constructed mutants ApcE(1-232), ApcE(63-240), ApcE(85-240) andApcE(121-240) and overexpressed the corresponding proteins. The experimental resultindicated that these mutant not only do not improve the water-solubility of proteins, but alsolose the function of autoassemblying with PCB.