A lectin from the Chinese bird-hunting spider binds sialic acids.

The affinity to sialic acid-containing oligosaccharides of the small-animal lectin SHL-I isolated from the venom of the Chinese bird-hunting spider Selenocosmia huwena is here described for the first time. By a strategic combination of NMR techniques, molecular modeling, and data mining tools it was possible to identify the crucial amino acid residues that are responsible for SHL-I's ability to bind sialic acid residues in a specific way. Furthermore, we are able to discuss the role of the functional groups of sialic acid when bound to SHL-I. Also the impact of Pro31 in its cis- or trans-form on SHL-I's ligand affinity is of special interest, since it answers the question if Trp32 is a crucial amino acid for stabilizing complexes between SHL-I and sialic acid. SHL-I can be considered as a proper model system that provides further insights into the binding mechanisms of small-animal lectins to sialic acid on a sub-molecular level.