Biosurfactants are amphiphilic compounds produced by microorganisms, and have been receiving increasing attention due to their unique properties compared to petroleum-based surfactants. Mannosylerythritol lipids (MELs), which are efficiently produced from vegetable oils by yeasts, are one of the most promising biosurfactants known [1, 2]. Recently, we have demonstrated that MEL-A, the major component of MELs, exhibits not only excellent surface-active and self-assembling properties [3] but also high binding affinity towards glycoproteins such as immunoglobulins and lectins [4]. However, available information on the binding manner is still limited. Considering the development of MEL-A into a new ligand for immunoglobulins, it is of great interest to characterize the molecular recognition further in detail. In this study, the binding between the self-assembled monolayer prepared from MEL-A and different immunoglobulins (IgG, IgM, and IgA) was investigated by a surface plasmon resonance (SPR) technique and an in-situ atomic force microscopy (AFM). We found that the glycolipid monolayers exhibit a high binding affinity towards all the immunoglobulins tested. The calculated binding constants of MEL-A with IgG, IgM and IgA were 9.4×10⁶ M^-1, 5.4×10⁶ M^-1, 7.2×10⁶ M^-1, respectively. Moreover, we succeeded in directly observing a large amount of immunoglobulin molecules bound to the monolayer with a markedly high density. Thus, MEL-A is very likely to have a great potential to serve as a novel affinity ligand on sensing and/or separation of immunoglobulins and related glycoproteins.

[1] Kitamoto et al., J. Biosci. Bioeng., 94, 187 (2002). [2] Morita et al., Appl. Microbiol. Biotechnol., 73, 305 (2006). [3] Imura et al., Langmuir, 23, 1659 (2007). [4] Konishi et al., Biotechnol. Lett., 29, 865 (2007).

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