NdhP and NdhQ: Two Novel Small Subunits of the Cyanobacterial NDH-1 Complex

The subunit composition of the NAD(P)H dehydrogenase complex of Thermosynechococcus elongatus was analyzed by different types of mass spectrometry. All 15 known subunits (NdhA-NdhO) were identified in the purified NDH-1L complex. Moreover, two additional intact mass tags of 4902.7 and 4710.5 Da could be assigned after reannotation of the T. elongatus genome. NdhP and NdhQ are predicted to contain a single transmembrane helix each, and homologues are apparent in other cyanobacteria. Additionally, ndhP is present in some cyanophages in a cluster of PSI genes and exhibits partial similarity to NDF6, a subunit of the plant NDH-1 complex.