Fluorescence resonance energy transfer mapping of subunit δ in spinach chloroplast F1 ATPase

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Abstract
Despite the considerable progress in the field of F0F1‐ATPases caused by solving the 2.8‐Å structure of mitochondrial F1 ATPase [Abrahams, J. P., Leslie, A. G. W., Lutter, R. & Walker, J. E. (1994) Nature 370, 621−628], little is known about the position and function of the enzyme's small subunits which were not resolved in the X‐ray analysis. We have previously genetically engineered Cys residues into the δ subunit of chloroplast F1 and used these mutant subunits in cross‐linking studies [Lill, H., Hensel, F., Junge, W. & Engelbrecht, S. (1996) J. Biol. Chem. 271, 32 737−32 742]. In this work, various fluorophores have been introduced into the mutant δ subunits and used in fluorescence‐resonance energy‐transfer measurements. The resulting distances were fitted into the framework of existing data. Subunit δ was found to be located between two α/β couples, stretching from the level of the nucleotide binding sites up to a position close to the N‐termini of subunits α and β. These results corroborate and further refine the previously found location of spinach CF1δ at the periphery and membrane‐distal part of CF1, where it may constitute a part of a stator in the rotatory machinery of F0F1.

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