A conserved human DJ1-subfamily motif (DJSM) is critical for anti-oxidative and deglycase activities of Plasmodium falciparum DJ1.

Plasmodium falciparum DJ1 (PfDJ1) belongs to the DJ-1/ThiJ/PfpI superfamily whose members are present in all the kingdoms of life and exhibit diverse cellular functions and biochemical activities. The common feature of the superfamily is the class I glutamine amidotransferase domain with a conserved redox-active cysteine residue, which mediates various activities of the superfamily members, including anti-oxidative activity in PfDJ1 and human DJ1 (hDJ1). As the superfamily members represent diverse functional classes, to investigate if there is any sequence feature unique to hDJ1-like proteins, sequences of the representative proteins of different functional classes were compared and analysed. A novel motif unique to PfDJ1 and several other hDJ1-like proteins, with the consensus sequence of TSXGPX5FXLX5L, was identified that we designated as the hDJ1-subfamily motif (DJSM). Several mutations that have been associated with Parkinson's disease are also present in DJSM, suggesting its functional importance in hDJ1-like proteins. Mutations of the conserved residues of DJSM of PfDJ1 did not significantly affect overall secondary structure, but caused both a significant loss (S151A and P154A) and gain (L168A) of anti-oxidative activity. We also report that PfDJ1 has deglycase activity, which was significantly decreased in its mutants of the catalytic cysteine (C106A) and DJSM (S151A and P154A). Episomal expression of the catalytic cysteine (C106A) or DJSM (P154A) mutant decreased growth rates of parasites as compared to that of wild type parasites or parasites expressing wild type PfDJ1. S151 appears to properly position the nucleophilic elbow containing C106 and P154 forms a hydrogen bond with C106, which could be a reason for the loss of activities of PfDJ1 upon their mutations. Taken together, DJSM delineates PfDJ1 and other hDJ1-subfamily proteins from the remaining superfamily, and is critical for anti-oxidative and deglycase activities of PfDJ1.

Identification of cyclin D3 as a new interaction partner of lamin A/C.

Lamin A/C is a major component of the nuclear lamina. An intact nuclear lamina has been proposed to be necessary for muscle differentiation. Cyclin D3 is known to be upregulated in differentiated muscle cells and to form insoluble complexes with cell-cycle regulatory factors in these cells. We have examined the possibility of direct binding interactions between lamin A/C and cyclin D3 by in vitro binding assays and co-immunoprecipitation studies with muscle cells. Our results indicate that cyclin D3 binds specifically to amino acid residues 383-474 of lamin A/C and associates with lamin A/C in muscle cells. The identification of cyclin D3 as a novel binding partner of lamin A/C has important implications for a role for lamin A/C in muscle differentiation.