Carbohydrate-lipid interactions: Affinities of methylmannose polysaccharides for lipids in aqueous solution

• Author(s) / Creator(s)

  • Xia, Li
  • Sun, Nian
  • Klassen, John S.
  • Liu, Lan
  • Bai, Yu
  • Lowary, Todd L.

• 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-5s, -8s, -11s and -14s), 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 (Ka) 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 Ka values are in the 104–105 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 (5×104) 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.

• Date created

  2012

• Subjects / Keywords

  • Carbohydrates
  • Lipids
  • Naphthenic acids
  • Polysaccharides
  • Electrospray ionization mass spectrometry

• Type of Item

  Article (Published)

• DOI

  https://doi.org/10.7939/R3ZK5611Q

• License

  © 2012 Liu, L., Bai, Y., Sun, N., Xia, L., Lowary, T. L., & Klassen, J. S. This version of this article is open access and can be downloaded and shared. The original author(s) and source must be cited.