IRKUTSK, RUSSIA

Institute of Plant Physiology and Biochemistry

Presumable redox control of phosphorylation of the mitochondrial chaperonin hsp60

--Subota, IY; Arziev, AS; Sengenko, LP; Tarasenko, VI; Konstantinov, YM

It was shown previously (MNL 80:14-15) that phosphorylation/dephosphorylation of serine/threonine or histidine residues of the target mitochondrial proteins through enzymatic activity of redox sensitive protein kinases and protein phosphatases in these organelles is presumably involved in metabolic response of mitochondria under the changes of redox conditions. To date redox-dependent phosphorylation of mitochondrial proteins has not been sufficiently elucidated. Although this modification has been observed in our experiments for at least 8 maize mitochondrial proteins (MNL 80:14-15), polypeptides nature and function of phosphorylation for these proteins remain poorly understood.

In this work, we revealed that one of mitochondrial phosphoproteins is heat shock protein 60 (hsp60).

The mitochondria were isolated from 3-day-old etiolated maize seedlings (hybrid VIR42MV) by a standard method of differential centrifugation. Protein phosphorylation assays were carried according to Struglics et al. (FEBS Lett. 475:213-217, 2000) with the use of [γ³²P]ATP (specific radioactivity was 6000 Ci/mmol).

Using immunoblotting with specific antibodies we have identified one from 8 mitochondrial phosphoproteins as mitochondrial chaperonin hsp60 (Fig. 1). It is well known that tetradecameric mitochondrial chaperonin hsp60 is required for ATP-dependent folding of precursor polypeptides and complex assembly. It prevents also aggregation and mediates protein refolding after heat shock. There is also some evidence on the function of hsp60 in the structure and transmission of mitochondrial DNA nucleoids in Saccharomyces cerevisiae (Kaufman et al., J Cell Biol 163:457-461, 2003). It was suggested previously high evolutionarily conserved function of this protein (Hemmingsen et al., Nature 333:330-334, 1988). We suggest that this evolutionarily conserved function of hsp60 is participation in redox regulation of genetic functions in mitochondria. Such an involvement of the chaperonin hsp60 in redox regulation of mitochondrial genome expression is possibly mediated by reversible redox-dependent phosphorylation.

Legends to figure

Fig.1. In vitro phosphorylation of redox-sensitive phosphoproteins including 66 kDa (A) were resolved by 12% SDS/PAGE and were immunoblotted (B) with antibody against hsp60.