Aldehydic nature and conformation of 3,6-anhydro-L-galactose monomer

作者：Lee Sun Bok^*; Lee Shin Youp; Lim Hyun Seung

来源：Biotechnology and Bioprocess Engineering, 2015, 20(5): 878-886.

DOI：10.1007/s12257-015-0520-3

• 3,6-anhydro-L-galactose
• open-chain aldehyde
• cis-trans conformation
• L-lactaldehyde dehydrogenase
• 3,6-anhydro-L-galactose dehydrogenase

We investigated the aldehydic nature and conformation of 3,6-anhydro-L-galactose (L-AnG) by using enzymes that bind L-AnG in a reactive conformation. We found that L-AnG, but not L-galactose, can be oxidized by E. coli L-lactaldehyde dehydrogenase (Ec_LADH); this observation suggests that L-AnG is an aldehyde belonging to the a-hydroxyaldehyde family. Because the native enzyme that catalyzes oxidation of L-AnG to its carboxylate is LAnG dehydrogenase (L-AnGDH), we compared the crystal structure and amino-acid sequences of Ec_LADH with those of L-AnGDHs. This analysis revealed that the two oxygen atoms in the a-hydroxyaldehyde moiety of L-AnG are essential for the reactions of Ec_LADH and LAnGDHs. A chemical database search indicated that two configurations of L-AnG are possible: a trans arrangement in which C-2 and C-5 hydroxyl groups are on the opposite side and a cis arrangement in which these groups are on the same side. Manual docking of the two forms of L-AnG into the active site of Pseudoalteromonas atlantica LAnGDH (Pa_L-AnGDH) revealed that only the trans LAnG configuration can be fitted into the active site of Pa_L-AnGDH. The identification of trans L-AnG suggests the existence of three L-AnG conformations: bicyclic pyranose, opened pyranose, and open-chain aldehyde. The conformation of L-AnG monomer (open-chain aldehyde) differs from that in agarose (bicyclic pyranose) or agarobiose (opened pyranose) because a five-membered anhydro ring is free to move and can find its most stable conformation. This study validates the assumption of trans-type open-chain aldehyde conformation of L-AnG that was applied in our previous studies.

• 出版日期2015-9