Mutational and nucleotide sequence analysis of S-adenosyl-L-homocysteine hydrolase from Rhodobacter capsulatus.
The genetic locus ahcY, encoding the enzyme S-adenosyl-L-homocysteine hydrolase (EC 3.3.1.1) from the bacterium Rhodobacter capsulatus, has been mapped by mutational analysis to within a cluster of genes involved in regulating the induction and maintenance of the bacterial photosynthetic apparatus. Sequence analysis demonstrates that ahcY encodes a 51-kDa polypeptide that displays 64% sequence identity to its human homolog. Insertion mutants in ahcY lack detectable S-adenosyl-L-homocysteine hydrolase activity and, as a consequence, S-adenosyl-L-homocysteine accumulates in the cells, resulting in a 16-fold decrease in the intracellular ratio of S-adenosyl-L-methionine to S-adenosyl-L-homocysteine as compared to wild-type cells. The ahcY disrupted strain fails to grow in minimal medium; however, growth is restored in minimal medium supplemented with methionine or homocysteine or in a complex medium, thereby indicating that the hydrolysis of S-adenosyl-L-homocysteine plays a key role in the metabolism of sulfur-containing amino acids. The ahcY mutant, when grown in supplemented medium, synthesizes significantly reduced levels of bacteriochlorophyll, indicating that modulation of the intracellular ratio of S-adenosyl-L-methionine to S-adenosyl-L-homocysteine may be an important factor in regulating bacteriochlorophyll biosynthesis.
Sganga
M W
MW
Department of Biology, Indiana University, Bloomington 47405.
Aksamit
R R
RR
Cantoni
G L
GL
Bauer
C E
CE
D043383:Adenosylhomocysteinase; D000595:Amino Acid Sequence; D001429:Bacteriochlorophylls / Q000096:biosynthesis; D001483:Base Sequence; D001665:Binding Sites; D004252:DNA Mutational Analysis; D005798:Genes, Bacterial; D006867:Hydrolases / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D015183:Restriction Mapping; D016354:Rhodobacter capsulatus / Q000235:genetics*; D016415:Sequence Alignment
D001429:Bacteriochlorophylls; D006867:Hydrolases; D043383:Adenosylhomocysteinase