STRUCTURAL MAPPING OF CYSTEINE-63 OF THE CHLOROPLAST ATP SYNTHASE BETA-SUBUNIT

The single sulfhydryl residue (cysteine-63) of the beta-subunit of the chloroplast ATP synthase F1 (CF1) was accessible to labeling reagents only after removal of the beta-subunit from the enzyme complex. This suggests that cysteine-63 may be located at an interface between the beta and the alpha-subunits of CF1, although alternative explanations such as a conformational change in beta brought about by its release from CF1 cannot be ruled out. Cysteine-63 was specifically labeled with [(diethylamino)methylcoumarinyl]-maleimide, and the distance between this site and trinitrophenyl-ADP at the nucleotide binding site on beta was mapped using fluorescence resonance energy transfer. Cysteine-63 is located in a hydrophobic pocket, 42 angstrom away from the nucleotide binding site on beta.