Biosynthesis of the cyclitol moiety of pyralomicin 1a in Nonomuraea spiralis MI178-34F18.
The biosynthetic pathway leading to the cyclitol moiety of pyralomicin 1a (1) in Nonomuraea spiralis MI178-34F18 has been studied using a series of 2H-labeled potential precursors. The results demonstrate that 2-epi-5-epi-valiolone (7), a common precursor for acarbose (4) and validamycin A (5) biosynthesis, is an immediate precursor of pyralomicin 1a. 5-epi-Valiolone (8) was also incorporated into 1, albeit less efficiently than 7. Other potential intermediates, such as valiolone (9), valienone (10), valienol (11), 1-epi-valienol (12), 5-epi-valiolol (13), and 1-epi-5-epi-valiolol (14) were not incorporated into pyralomicin 1a. To explain this surprising observation, it is proposed that either 2-epi-5-epi-valiolone (7) is specifically activated (e.g., to its phosphate) and that the further transformations take place on activated intermediates (which can not be generated directly from their unactivated counterparts), or that the transformation of 7 into 1 involves a substrate-channeling mechanism in which enzyme-bound intermediates are directly transferred from one enzyme active site to the next in a multi-enzyme complex.
Institute of Microbial Chemistry, 14-23, Kamiosaki 3-chome, Shinagawa-ku, Tokyo 141-0021, Japan. naganawah@bikaken.or.jp
Hiroshi
H
Naganawa
Hideki
H
Hashizume
Yumiko
Y
Kubota
Ryuichi
R
Sawa
Yoshikazu
Y
Takahashi
Kenji
K
Arakawa
Simeon G
SG
Bowers
Taifo
T
Mahmud
D000192:Actinomycetales / Q000378:metabolism*; D002240:Carbohydrate Sequence; D002867:Chromones / Q000302:isolation & purification / Q000378:metabolism*; D005285:Fermentation; D008969:Molecular Sequence Data; D011758:Pyrroles / Q000302:isolation & purification / Q000378:metabolism*
D002867:Chromones; D011758:Pyrroles; C101442:pyralomicin 1a