In cyanobacteria, phycobiliproteins (PBS) show excellent energy transfer among the chromophores absorbing over most of the visible. The energy transfers are used to study phycobilisome assembly and bioimaging. Using All4261GAF2(C81L) as energy donor, ApcE(1-240/Delta 87-130) as enemy acceptor, we co-expressed fusion protein ApcE(1-240/Delta 87-130)::All4261GAF2(C81L) with phycobiliprotein in Escherichia Coli and studied the energy transfer between two protein domains. With N-terminal His6 tag, ApcE(1-240/Delta 87-130)::All4261GAF2(C81L) cannot be purified by nickel-affinity column. We added six histidines in the C-terminal of ApcE(1-240/Delta 87-130)::All4261GAF2(C81L) and co-expressed it with phycobiliprotein. ApcE(1-240/Delta 87-130)::PCB-All4261GAF2(C81L)(His6) was purified successfully and only singly chromophorylated at All4261GAF2(C81L)(His6) domain. The singly chromophorylate ApcE(1-240/Delta 87-130)::PCB-All4261GAF2(C81L)(His6) was incubated with fresh PCB and the doubly chromophorylated PCB-ApcE(1-240/Delta 87-130)::PCB-All4261GAF2(C811-)(His6) was obtained. The double chromophored fusion protein absorbed light in the range of 615-660 nm, and fluoresced only at 668 nm. Photochemistry analysis showed that excitation energy transfer from the short-wavelength absorbing at All4261-GAF2(C81L) domain was achieved successfully to the long-wavelength absorbing at the ApcE(1-240/Delta 87-130) domain. (C) 2016 Published by Elsevier Inc.