PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

Structure and function of the orange carotenoid protein. Cheryl Kerfeld¹, David Krogmann^*,2, Michael Sawaya¹, Todd Yeates¹, ¹ Molecular Biology Institute, Los Angeles, CA, USA² Department of Biochemistry, West Lafayette, IN, USA

ABSTRACT- There have been numerous reports of carotenoid proteins in cyanobacteria. The structure of the uniquely water-soluble orange carotenoid-binding protein (OCP) isolated from the cyanobacterium Arthrospira maxima has been determined at a resolution of 2.1. The OCP is the first structural example of a protein that binds exclusively carotenoids. The structure reveals the protein-pigment interactions that influence the spectral properties of the carotenoid. The OCP appears to be involved in photoprotection, and may also function as a carotenoid transport protein. Data from our laboratory indicates the OCP is an avid quencher of singlet oxygen. A proteolytic product of OCP has been isolated that appears red instead of orange. The OCP can also be converted into a red protein by exposure to low pH. Circular dichroism data suggest that low pH changes the structure of the protein. Details of the interaction between the pigment and protein will be discussed in the context of the putative photoprotective function of the OCP.

KEY WORDS: pigment-protein, carotenoid, photoprotection, crystallography