The sodium ion translocating oxaloacetate decarboxylase of Klebsiella pneumoniae. Sequence of the integral membrane-bound subunits beta and gamma.

The sequences upstream and downstream of the cloned gene for the alpha-subunit of the Na+ pump oxaloacetate decarboxylase of Klebsiella pneumonia were determined. An open reading frame in the upstream region was identified as the gene for the gamma-subunit, and an open reading frame in the downstream region represents the gene for the beta-subunit. The deduced primary structure of the gamma- and beta-subunit was confirmed by protein sequencing of about 37 and 22%, respectively, of each polypeptide chain. The gene for the gamma-subunit has a GC content of 64% and codes for 83 amino acids. The protein is not processed at its amino terminus or at its carboxyl terminus. The gene for the beta-subunit has a GC content of 66% and codes for 327 amino acids. The protein contains a blocked aminoterminal methionine residue. Whether processing occurs at the carboxyl terminus is unknown. Hydropathy calculations defined one transmembrane helix in the amino-terminal part of the gamma-subunit and a hydrophilic carboxyl-terminal part that is certainly not embedded within the lipid bilayer. A proline- and alanine-rich sequence in the carboxyl-terminal part may provide the protein with conformational flexibility. According to hydropathy and acrophilicity calculations, the secondary structure of the beta-subunit may be formed with 5 or 6 intramembrane helical segments.