A nested gene in Streptomyces bacteria encodes a protein involved in quaternary complex formation.
The gene pgaM is involved in the biosynthesis of an angucycline-type polyketide antibiotic in Streptomyces sp. PGA64. It encodes a two-domain polypeptide consisting of an N-terminal flavoprotein oxygenase and a C-terminal short-chain alcohol dehydrogenase/reductase, which are fused together at the translational level as a result of end codon deletion. Here we show that translation also initiates at an internal start codon that enables independent expression of a separate reductase subunit, PgaMred. This confirms that the gene exhibits a rare viral-like arrangement of two overlapping reading frames that allows simultaneous expression of two alternative forms of the protein. Together, these two proteins associate to form a stable non-covalent complex, the native form of PgaM. The reductase subunit PgaMred is shown to provide enzyme stability and to affect the redox state of the oxygenase domain FAD. Finally, a model for the quaternary structure of the complex that explains the necessity for a nested gene system and the unusual behaviour of the protein subunits in vitro is presented.
Kallio
Pauli
P
Department of Biochemistry and Food Chemistry, University of Turku, FIN-20014 Turku, Finland.
Liu
Zhanliang
Z
Mäntsälä
Pekka
P
Niemi
Jarmo
J
Metsä-Ketelä
Mikko
M
D000426:Alcohol Dehydrogenase / Q000737:chemistry; D000595:Amino Acid Sequence; D001483:Base Sequence; D002384:Catalysis; D018387:Codon, Initiator; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D007527:Isoenzymes; D006899:Mixed Function Oxygenases / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D032041:Nested Genes; D016366:Open Reading Frames; D010084:Oxidation-Reduction; D010957:Plasmids; D048630:Polyketide Synthases / Q000096:biosynthesis; D020836:Protein Structure, Quaternary / Q000235:genetics*; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D011506:Proteins / Q000235:genetics*; D020539:Sequence Analysis, Protein; D013302:Streptomyces / Q000235:genetics*
D018387:Codon, Initiator; D007527:Isoenzymes; D021122:Protein Subunits; D011506:Proteins; D048630:Polyketide Synthases; D006899:Mixed Function Oxygenases; D000426:Alcohol Dehydrogenase