My research is focused on the structural characterization of carotenoid-binding proteins in cyanobacteria through various methods like biochemical analysis, genetic engineering, and X-ray crystallography. Carotenoid-binding proteins are essential for the photoprotection process that occurs when cyanobacteria are exposed to excess light. The orange carotenoid protein (OCP) plays a crucial role in this process by dissipating the absorbed light energy as heat. The OCP physically attaches to the phycobilisome (PBS), preventing energy transfer to the photosynthetic reaction centers (RCs). The OCP contains two domains – an active N-terminal domain (NTD) and a regulatory C-terminal domain (CTD). Homologs of the CTD (CTDH) are suggested to uptake carotenoids from the thylakoid membrane and transfer the carotenoid to helical carotenoid proteins (HCPs), which are paralogs of the NTD. Holo-HCPs have various functions such as carotenoid carriers, singlet oxygen quenchers, and energy quenching proteins. However, some of their unique crystal structures have not been solved yet. Our primary objectives are to determine the high-resolution crystal structures of the holo/apo-OCP homologs and investigate the mechanism of carotenoid binding and transfer from membranes.