STRUCTURAL BASIS FOR A UNIQUE ATP SYNTNASE CORE COMPLEX FROM NANOARCHAEUM EQUITANS

Abstract

Archaeal ATP synthases are the oldest yet least studied amongst the ATP synthases. Genomic interrogation of the archaeal parasite, Nanoarchaeum equitans showed that it lacks several genes representing ATP synthase subunits, suggesting that it is minimalistic or has lost these genes due to parasitic dependency. We report the crystal structure and biophysical studies of the regulatory subunit NeqB, the nucleotide free and bound hexameric complex, NeqAB to understand the functionality of this complex. We found that NeqB is shorter than its homologues yet forms a similar catalytic core with NeqA. The NeqAB complex assumes a closed conformation, irrespective of nucleotide binding, which goes against the binding change mode of catalysis. ATPase assays indicated a lack of significant hydrolysis by the core complex. Together, our findings show that, although N. equitans possesses an assembled ATP synthase hexameric core A3B3, it does not function as a bona fide ATP synthase in vitro.