Identification, expression level and characterization of mouse glutaredoxin 2 isoforms

HUDEMANN, C.; LÖNN, M.; REY FUNES, M.; H. COIRINI,; F. CAPANI,; A. HOLMGREN; C.H. LILLIG

Nynäshamn, Suecia

Conferencia; MBB-Conference 2006; 2006

MBB

Glutaredoxin 2 (Grx2) is a glutathione-dependent oxidoreductase with high specificity for glutathione-mixed disulfides that facilitates the maintenance of mitochondrial redox homeostasis upon oxidative stress-induced apoptosis. Grx2 was first characterized as mitochondrial protein, but alternative splice variants lacking the transit peptide-encoding first exon were proposed for both the human and mouse gene. Here, we have systematically screened for new transcript variants of mouse Grx2 and identified a total of six exons. Three constitutive exons (II, III, and IV) encode the basic Grx structure. In addition, we found two alternative first exons (exons Ia and Ic), that both contain alternative splice donor sites, and one single cassette exon (exon IIIb) located between exons III and IV. Both exons Ic and IIIb are unique to the mouse gene and not present in the human counterpart. Vice versa, the mouse gene does not contain a region homologous to human exon Ib. The six exons give rise to five different transcript variants, which encode three different protein isoforms: (1) the previously established mitochondrial Grx2a, (2) the ubiquitously expressed cytosolic Grx2c and (3) the testis-specific, cytosolic isoform Grx2d. As demonstrated for human Grx2 before, mouse Grx2c can form an iron sulfur cluster-bridged dimer and is enzymatically active as monomer. Grx2d lacks parts of the substrate binding sites and one of the additional cysteinyl residues necessary to complex the [Fe,S]-cluster. Grx2d was not expressed in soluble form in E. coli. The renatured protein was enzymatically inactive and did not cross react with the Grx2 antibody. Testis lack Grx2a, but contain both Grx2c and Grx2d. Prominent immunostaining was detected in spermatogonia and spermatids. Our results imply additional functions of Grx2 during oxidative stress and in cellular differentiation.