Subunit delta of chloroplast F0F1-ATPase and OSCP of mitochondrial F0F1-ATPase: a comparison by CD-spectroscopy.

CD spectra have been recorded with subunit delta from chloroplast CF0CF1 and with OSCP from mitochondrial MF0MF1. These subunits are supposed to act similarly at the interface between proton transport through the F0-portion and ATP-synthesis in the F1-portion of their respective F0F1-ATPase. Evaluation of the data for both proteins revealed a very high alpha-helix content of approximately 85% and practically no beta-sheets. Despite their low homology on the primary structure level (23% identity) and their different electrostatic properties (pI-values differ by 3 units), spinach delta and porcine OSCP are indistinguishable with respect to their secondary structure as measured by CD. Prediction and analysis of consensual alpha-helices even in poorly conserved regions indicate a high degree of structural similarity between chloroplast delta and OSCP. In view of the topology and function of delta and OSCP in intact F0F1 these findings are interpreted to indicate the dominance of secondary and tertiary structure over the primary structure in their supposed function between proton flow and ATP-synthesis.