Antibodies against F1-ATPase alpha-subunit recognize mitochondrial chaperones. Evidence for an evolutionary relationship between chaperonin and ATPase protein families.

Antibodies raised against two synthetic peptides from rat liver F1-ATPase alpha-subunit sequence recognized two main heat-shock proteins from Drosophila (p71 and p56) and rat liver (p74 and p54) cells. One of the antisera showed a 20-fold higher reactivity toward Escherichia coli GroEL chaperonin than toward the alpha-subunit purified from Drosophila. Indirect immunofluorescence microscopy and subcellular fractionation experiments located both mammalian heat-shock proteins in the mitochondria. The recent findings of functional homology between chaperonins and alpha-subunits, together with the unsuspected immunological reactivity of two mitochondrial molecular chaperones toward antisera derived from two different sequence motifs of the alpha-subunit, strongly argue in favor of the existence of an evolutionary relationship between chaperonins and alpha-subunits. The complete sequence alignment of F-type ATPase alpha-subunits and chaperonins revealed the existence of eleven most conserved regions (approximately 30% of each protein sequence) with an overall amino acid identity of 20 +/- 2% and similarity of 39 +/- 4%. A search of protein data bases with three different consensus sequences derived from this alignment identified a significant proportion of proteins belonging only to these two protein families. Since the alpha-subunit protein family is evolutionary related to the other catalytic (A and beta) and regulatory (B) subunits of V- and F-type ATPases, the homology reported herein allowed us to analyze, in the chaperonin sequences, the conservation of critical residues involved in nucleotide binding. These data support the hypothesis that chaperonins and the major subunits of V- and F-type ATPases are evolutionary related.