Biology

Dr. Dileep Vasudevan
Institute of Life Sciences, Bhubaneswar

Abstract:

FK506-binding protein (FKBP) family are ubiquitously found in all life forms, ranging from prokaryotes to higher eukaryotes. Arabidopsis thaliana possesses seven multi-domain FKBPs. AtFKBP53 is a multi-domain FKBP that gets localized into the nucleus. It is known to have a conserved peptidyl-prolyl isomerase (PPIase) domain characteristic of all FKBPs, at the C-terminus and a highly charged N-terminal stretch, which binds to the histone H3 and has been proposed to perform the function of a histone chaperone. To understand the molecular details of this PPIase with histone chaperoning activity, we have solved the crystal structures of its terminal domains and have functionally characterized them. The crystal structure of the C-terminal domain was solved in complex with FK-506 compound and it revealed the typical monomeric fold of an FK506-binding domain. Moreover, the C-terminal domain showed strong PPIase activity, and no role in histone chaperoning. The N-terminal domain on the other hand had a pentameric nucleoplasmin-fold; making this the first report of a plant nucleoplasmin structure. Further characterization revealed the N-terminal nucleoplasmin domain to interact with H2A/H2B and H3/H4, simultaneously, suggesting two different binding sites for the histone oligomers. Plasmid supercoiling assay showed the pentameric domain to assist nucleosome assembly, and thus a functional histone chaperone. While exploring the role of the nucleoplasmin domain in a possible nucleosome disassembly function, we noticed that it forms a discrete complex with pre-formed nucleosomes, rather than causing destabilization.