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Carbohydrate–Lipid Interactions: Affinities of Methylmannose Polysaccharides for Lipids in Aqueous Solution
Author(s) -
Liu Lan,
Bai Yu,
Sun Nian,
Xia Li,
Lowary Todd L.,
Klassen John S.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201201222
Subject(s) - affinities , polysaccharide , chemistry , carbohydrate , aqueous solution , biochemistry , organic chemistry
Abstract The interactions between 3‐ O ‐methyl‐mannose polysaccharides (MMPs), extracted from Mycobacterium smegmatis (consisting of a mixture of MMP‐10, ‐11, ‐12 and ‐13) or obtained by chemical synthesis (MMP‐5 s , ‐8 s , ‐11 s and ‐14 s ), and linear saturated and unsaturated fatty acids (FAs), and a commercial mixture of naphthenic acids (NAs) in aqueous solution at 25 °C and pH 8.5 were quantified by electrospray ionization mass spectrometry (ESI‐MS). Association constants ( K a ) for MMP binding to four FAs (myristic acid, palmitic acid, stearic acid and trans ‐parinaric acid) were measured by using an indirect ESI‐MS assay, the “proxy protein” method. The K a values are in the 10 4 –10 5 M −1 range and, based on results obtained for the binding of the synthetic MMPs with palmitic acid, increase with the size of the carbohydrate. Notably, the measured affinity of the extracted MMPs for trans ‐parinaric acid is two orders of magnitude smaller than the reported value, which was determined by using a fluorescence assay. Using a newly developed competitive binding assay, referred to as the “proxy protein/proxy ligand” ESI‐MS method, it was shown that MMPs bind specifically to NAs in aqueous solution, with apparent affinities of approximately (5×10 4 ) M −1 for the mixture of NAs tested. This represents the first demonstration that MMPs can bind to hydrophobic species more complex than those containing linear alkyl/alkenyl chains. Moreover, the approach developed here represents a novel method for probing carbohydrate–lipid interactions.