Adhesion forces in the self-recognition of oligosaccharide epitopes of the proteoglycan aggregation factor of the marine sponge Microciona prolifera |
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Authors: | Adriana Carvalho de Souza Dragomir N. Ganchev Margot M. E. Snel Jan P. J. M. van der Eerden Johannes F. G. Vliegenthart Johannis P. Kamerling |
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Affiliation: | Bijvoet Center, Department of Bio-Organic Chemistry, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands. |
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Abstract: | Cell aggregation in the marine sponge Microciona prolifera is mediated by a multimillion molecular-mass aggregation factor, termed MAF. Earlier investigations revealed that the cell aggregation activity of MAF depends on two functional domains: (i) a Ca2+-independent cell-binding domain and (ii) a Ca2+-dependent proteoglycan self-interaction domain. Structural analysis of involved carbohydrate fragments of the proteoglycan in the self-association established a sulfated disaccharide β-d-GlcpNAc3S-(1→3)-α-l-Fucp and a pyruvated trisaccharide β-d-Galp4,6(R)Pyr-(1→4)-β-d-GlcpNAc-(1→3)-α-l-Fucp. Recent UV, SPR, and TEM studies, using BSA conjugates and gold nanoparticles of the synthetic sulfated disaccharide, clearly demonstrated self-recognition on the disaccharide level in the presence of Ca2+-ions. To determine binding forces of the carbohydrate–carbohydrate interactions for both synthetic MAF oligosaccharides, atomic force microscopy (AFM) studies were carried out. It turned out that, in the presence of Ca2+-ions, the force required to separate the tip and sample coated with a self-assembling monolayer of thiol-spacer-containing β-d-GlcpNAc-(1→3)-α-l-Fucp-(1→O)(CH2)3S(CH2)6S- was found to be quantized in integer multiples of 30 ± 6 pN. No binding was observed between the two monolayers in the absence of Ca2+-ions. Cd2+-ions could partially induce the self-interaction. In contrast, similar AFM experiments with thiol-spacer-containing β-d-Galp4,6(R)Pyr-(1→4)-β-d-GlcpNAc-(1→3)-α-l-Fucp-(1→O)(CH2)3S(CH2)6S- did not show a binding in the presence of Ca2+-ions. Also TEM experiments of gold nanoparticles coated with the pyruvated trisaccharide could not make visible aggregation in the presence of Ca2+-ions. It is suggested that the self-interaction between the sulfated disaccharide fragments is stronger than that between the pyruvated trisaccharide. |
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Keywords: | Carbohydrate– carbohydrate interactions Atomic force microscopy Transmission electron microscopy Marine sponges Cell adhesion |
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