Cyanobacteriochrome covalently binds a linear tetrapyrrole molecule in the GAF domain. The A-ring of linear tetrapyrrole molecule is anchored at cysteine residue in the GAF domain via thioethel bond. The GAF domain of cyanobacteriochrome is related to phytochrome GAF, however, These GAF domains are distinct. A second cysteine linkage to the tetrapyrrole is found in some cyanobacteriochrome GAF domains resulting in blue-green photo reversible light sensitivity
They perform reversible photoconversion between green(~530 nm)- and red-(~660 nm) absorbing forms or between blue(~430 nm)- and green-absorbing forms. These spectral properties significantly differ from that of phytochrome which photoconverts between red- and far-red(~700 nm)-absorbing forms.
- Ikeuchi, M; T Ishizuka (2008-10-07). "Cyanobacteriochromes: a new superfamily of tetrapyrrole-binding photoreceptors in cyanobacteria". Photochemical & Photobiological Sciences. RSC Publishing. 7 (10): 1159–67. doi:10.1039/b802660m.
- Rockwell, Nathan C.; Njuguna, Stephanie Lane; Roberts, Laurel; Castillo, Elenor; Parson, Victoria L.; Dwojak, Sunshine; Lagarias, J. Clark; Spiller, Susan C. (2008-07-08). "A second conserved GAF domain cysteine is required for the blue/green photoreversibility of cyanobacteriochrome Tlr0924 from Thermosynechococcus elongatus". Biochemistry. 47 (27): 7304–7316. doi:10.1021/bi800088t. ISSN 0006-2960. PMC 2574597. PMID 18549244.