Biosynthesis of (7-mercaptoheptanoyl)threonine phosphate

The biosynthesis of (7-mercaptoheptanoyl)threonine phosphate (HS-HTP) has been studied in the methanogenic bacteria Methanococcus volta and Methanosarcina thermophila. Growth of these cells in medium containing [7,7-2H2]-7-mercaptoheptanoic acid, [3,4,4,4-threonine-2H4]-N-(7-mercaptoheptanoyl)threonine, [7,7-2H2]-N-(7-mercaptoheptanoyl)threonine, or DL-[3,4,4,4-2H4]threonine led to the generation of labeled HS-HTP containing a portion of the molecules with the same number of deuteriums as the precursor molecule. This result indicated that each of these labeled molecules can serve as a precursor for the biosynthesis of HS-HTP. Cell-free extracts of these methanogens were shown to carry out the ATP-dependent phosphorylation of N-(7-mercaptoheptanoyl)threonine to HS-HTP. These observations indicate that the biosynthesis of HS-HTP involves the coupling of mercaptoheptanoic acid with threonine to form (7-mercaptoheptanoyl)threonine, which is then phosphorylated to HS-HTP.