The mitochondrial proteins AtHscB and AtIsu1 involved in Fe–S cluster assembly interact with the Hsp70-type chaperon AtHscA2 and modulate its catalytic activity

• We generated the recombinant proteins AtHscA2, the co-chaperone (AtHscB) and the scaffold protein (AtIsu1) of A. thaliana
• We characterized the interaction among these proteins in vitro
• We characterized the effect of the AtHscB and AtIsu1 on the ATPase activity of the AtHscA2 in vitro

Arabidopsis plants contain two genes coding for mitochondrial Hsp70-type chaperon-like proteins, AtHscA1 (At4g37910) and AtHscA2 (At5g09590). Both genes are homologs of the Ssq1 gene involved in Fe–S cluster assembly in yeast. Protein–protein interaction studies showed that AtHscA2 interacts with AtIsu1 and AtHscB, two Arabidopsis homologs of the Isu1 protein and the Jac1 yeast co-chaperone. Moreover, this interaction could modulate the activity of AtHscA2. In the presence of a 1:5:5 molar ratio of AtHscA2:AtIsu1:AtHscB we observed an increase in the Vmax and a decrease in the S0.5 for ATP of AtHscA2. Furthermore, an increase of about 28-fold in the catalytic efficiency of AtHscA2 was also observed. Results suggest that AtHscA2 in cooperation with AtIsu1 and AtHscB play an important role in the regulation of the Fe–S assembly pathway in plant mitochondria.