Recognition of acetylated oligosaccharides by human L-ficolin

Abstract

The complement system is a protein cascade capable of neutralizing invading pathogens. One of its activation pathways is the lectin pathway which is dependent on the binding of MBL or the ficolins. The specificity of L-ficolin binding has been investigated previously and it was observed that binding is dependent on acetyl groups. If this was the only requirement this would enable L-ficolin to bind to most mammalian glycosylations since they contain acetylated monosaccharides. To investigate this further L-ficolin was subjected to glycan-array analysis in which L-ficolin binding to 279 different glycans was investigated. Few of these bound L-ficolin above background level but clear structural requirements were discovered.

Figure 1

Purified L-ficolin analyzed reduced and non-reduced on SDS-PAGE and subsequently stained with Coomassie Brilliant Blue. When run reduced on SDS-PAGE L-ficolin polypeptide chains are found only in the 35 kDa band. Non-reduced three L-ficolin bands could be identified at 35 kDa and two of more than 212 kDa. The top bands are homomultimeric complexes held together by disulphide bridges while the 35 kDa band is composed of non-covalently attached L-ficolin polypeptide chains.

Figure 2

L-ficolin binding to the different carbohydrate structures on the glycan array chip. The relative fluorescence indicates the amount of bound L-ficolin to each of the individual glycans. The error bars indicate the standard error of measurement. The numbered arrows points to the three best L-ficolin binding glycans and their exact chemical structure is shown.