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 F-1-AT Pase alpha-subunit sequence recognized two main heat-shock proteins fr om Drosophila (p71 and p56) and rat liver (p74 and p54) cells. One of the antisera showed a 20-fold higher reactivity toward Escherichia col i GroEL chaperonin than toward the cu-subunit purified from Drosophila . Indirect immunofluorescence microscopy and subcellular fractionation experiments located both mammalian heat-shock proteins in the mitocho ndria. The recent findings of functional homology between chaperonins and alpha-subunits, together with the unsuspected immunological reacti vity of two mitochondrial molecular chaperones toward antisera derived from two different sequence motifs of the alpha-subunit, strongly arg ue in favor of the existence of an evolutionary relationship between c haperonins and alpha-subunits. The complete sequence alignment of F-ty pe ATPase alpha-subunits and chaperonins revealed the existence of ele ven most conserved regions (similar to 30% of each protein sequence) w ith an overall amino acid identity of 20 +/- 2% and similarity of 39 /- 4%. A search of protein data bases with three different consensus s equences derived from this alignment identified a significant proporti on of proteins belonging only to these two protein families. Since the alpha-subunit protein family is evolutionary related to the other cat alytic (A and beta) and regulatory (B) subunits of V- and F-type ATPas es, the homology reported herein allowed us to analyze, in the chapero nin sequences, the conservation of critical residues involved in nucle otide binding. These data support the hypothesis that chaperonins and the major subunits of V- and F-type ATPases are evolutionary related.