The role of the amino-terminal beta-barrel domain of the alpha and beta subunits in the yeast F-1-ATPase

The crystal structure of mitochondrial F-1-ATPase indicates that the alpha and beta subunits fold into a structure defined by three domains: the top b eta-barrel domain, the middle nucleotide-binding domain, and the C-terminal alpha-helix bundle domain (Abrahams et al., 1994); Bianchet et al., 1998). The beta-barrel domains of the alpha and beta subunits form a crown struct ure at the top of F-1, which was suggested to stabilize it (Abrahams et al. 1994). In this study, the role of the beta-barrel domain in the alpha and beta subunits of the yeast Saccharomyces cerevisiae F-1, with regard to its folding and assembly, was investigated. The beta-barrel domains of yeast F -1 alpha and beta subunits were expressed individually and together in Esch erichia coli. When expressed separately, the P-barrel domain of the beta su bunit formed a large aggregate structure, while the domain of the alpha sub unit was predominately a monomer or dimer. However, coexpression of the bet a-barrel domain of alpha subunit with the beta-barrel domain of beta subuni t, greatly reduced the aggregation of the beta subunit domain. Furthermore, the two domains copurified in complexes with the major portion of the comp lex found in a small molecular weight form. These results indicate that the beta-barrel domain of the alpha and beta subunits interact specifically wi th each other and that these interactions prevent the aggregation of the be ta-barrel domain of the beta subunit. These results mimic in vivo results a nd suggest that the interactions of the beta-barrel domains may be critical during the folding and assembly of F-1.