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KMID : 1094720150200050878
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Biotechnology and Bioprocess Engineering
2015 Volume.20 No. 5 p.878 ~ p.886
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Aldehydic nature and conformation of 3,6-anhydro-L-galactose monomer
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Lee Sun-Bok
Lee Shin-Youp
Lim Hyun-Seung
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Abstract
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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.
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KEYWORD
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3,6-anhydro-L-galactose, open-chain aldehyde, cis-trans conformation, L-lactaldehyde dehydrogenase, 3,6-anhydro-L-galactose dehydrogenase
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