Maize Genetics Cooperation Newsletter vol 81 2007

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 is presumably involved in the 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), the nature of the polypeptides and the function of phosphorylation for these proteins remain poorly understood. In this work, we show that one of the mitochondrial phosphoproteins is the heat shock protein 60 (hsp60).

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

By immunoblotting with specific antibodies, we have identified one of 8 mitochondrial phosphoproteins as mitochondrial chaper-

Figure 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.

onin hsp60 (Fig. 1). Mitochondrial chaperonin hsp60 is required for ATP-dependent folding of precursor polypeptides and complex assembly. It also prevents aggregation and mediates protein refolding after heat shock. There is also some evidence of hsp60 involvement in the structure and transmission of mitochondrial DNA nucleoids in Saccharomyces cerevisiae (Kaufman et al., J. Cell. Biol. 163:457-461, 2003). We suggest that this evolutionarily conserved hsp60 participates in redox regulation of mitochondrial genome expression and is possibly mediated by reversible redox-dependent phosphorylation.

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