Chlorophyll Binding Ability of Non-chloroplastic DUF538 Protein Superfamily in Plants

The type-1 water soluble chlorophyll binding proteins (WSCP1) have been generally known as chlorophyll extractors and transporters from the thylakoid membrane to the chloroplast envelope, where the membrane bound chlorophyllase catabolizes the chlorophyll. Despite the type-2 WSCP, WSCP1 has been known to be located in the chloroplasts of the green plants. In the present study, the non-chloroplastic protein superfamily containing domain of unknown function 538 (DUF538) as functional homologue of type-1 WSCP has been identified in plants. The structural similarities/differences and the cellular locations of Celosia cristata DUF538 and Chenopodium album WSCP1 were predicted by using computational tools and the chlorophyll binding abilities of their purified maltose binding protein-fused forms were estimated by maltose binding affinity method. It was predicted that despite CaWSCP1, CcDUF538 is a non-chloroplastic protein. The chlorophyll binding abilities of the recombinant fusion forms of test WSCP1 and DUF538 were estimated to be about 58 and 56%, respectively. Considering DUF538 as stress-induced protein, it was speculated that they may form complex with chlorophyll molecules or their hydrolyzed products out of chloroplasts to proceed the chlorophyll breakdown and nitrogen/carbon recycling in stress-challenged plants. © 2016, The National Academy of Sciences, India.