Role of short conserved segments of α- and β-subunits that link F1-ATPase catalytic and noncatalytic sites

Abstract

An analysis of amino acid sequences and 3D structures of chloroplast, mitochondrial, and bacterial F(1)-ATPases revealed that in their alpha- and beta-chains there are short highly conserved segments linking in pairs the catalytic and noncatalytic sites. The analysis was based on the reported effect of directed mutagenesis of amino acids forming these segments on catalytic properties of the F(1)-ATPases. It is proposed that one of these segments is responsible for transduction of a conformation signal from the noncatalytic to catalytic site upon ADP-for-ATP substitution at the noncatalytic site. At the catalytic site, this signal changes position of the terminal amino acid residue with respect to the adenine part of the molecule and results in a lower tightness of MgADP binding and its dissociation followed by enzyme activation. Mutagenesis of amino acids comprised by the two other segments was shown to produce an effect on the rate of cooperative catalysis, whereas the rate of single-site catalysis remained unaffected. This suggests that these segments are responsible for the cooperative mode of enzyme functioning.