Crystallization and preliminary analysis of the NqrA and NqrC subunits of the Na⁺-translocating NADH:ubiquinone oxidoreductase from<i>Vibrio cholerae</i>

The Na + -translocating NADH:ubiquinone oxidoreductase (Na + -NQR) from Vibrio cholerae is a membrane protein complex consisting of six different subunits NqrA–NqrF. The major domains of the NqrA and NqrC subunits were heterologously expressed in Escherichia coli and crystallized. The structure of NqrA 1–377 was solved in space groups C 222 1 and P 2 1 by SAD phasing and molecular replacement at 1.9 and 2.1 Å resolution, respectively. NqrC devoid of the transmembrane helix was co-expressed with ApbE to insert the flavin mononucleotide group covalently attached to Thr225. The structure was determined by molecular replacement using apo-NqrC of Parabacteroides distasonis as search model at 1.8 Å resolution.