N-terminal processing of membrane-targeted MnSOD and formation of multiple active superoxide dismutase dimers in the nitrogen-fixing cyanobacterium Anabaena sp strain PCC7120

作者：Raghavan Prashanth S; Rajaram Hema^*; Apte Shree K

来源：FEBS Journal, 2013, 280(19): 4827-4838.

DOI：10.1111/febs.12455

• Anabaena
• membrane-targeted protein processing
• MnSOD
• nitrogen fixation
• oxidative stress

Anabaena sp. strain PCC7120 expresses a 30kDa manganese-dependent superoxide dismutase (MnSOD) comprising a hydrophobic region (signal peptide + linker peptide) attached to a catalytic unit. Bioinformatics predicted cleavage of the signal peptide at (25)CQPQ by signal peptidase and of the linker peptide by an Arg-C-like protease at the Arg52/Arg59 residue. The three predicted forms of MnSOD were immunodetected in Anabaena, with the 30kDa MnSOD found exclusively in the membrane and the shorter 27 and 24kDa forms found both in the membrane and soluble fractions. The corresponding sodA gene was truncated for (a) the first eight residues, or, (b) the signal peptide, or (c) the entire hydrophobic region, or (d) the Arg52/Arg59 residues were modified to serine. Overexpression of these MnSOD variants in recombinant Anabaena strains revealed that (a) the 30kDa membrane-targeted MnSOD was cleaved by membrane-localized signal peptidase either during or after its transport through the membrane to release the 27kDa form, either in the cytosol or in the periplasmic/thylakoid lumen, (b) the 27kDa form was further cleaved to the 24kDa form by Arg-C-like protease, both in the cytosol and in the periplasmic/thylakoid lumen, (c) deletion of signal peptide localized the MnSOD forms in the cytosol, and (d) alteration of the signal/linker peptide cleavage sites interfered with MnSOD localization and processing. Homo/heterodimerization of the 24 and 27kDa forms of MnSOD and the cytosolic iron-dependent SOD results in multiple SOD activities, from a single MnSOD gene (sodA), in different cellular compartments of Anabaena.

• 出版日期2013-10