Fig. 2.

Defining motifs and families of motifs. A, Motif types. Fixed substructures are continuous units of defined monosaccharides. Intolerant definitions require the unit to be unsubstituted, and tolerant definitions allow substitutions. Explicit definitions define the locations where substitutions are optional, which gives the highest level of precision in the definition. Variable substructures allow for options in the monosaccharides, providing another level of flexibility in the definition. Non-contiguous substructures allow the components of a motif to be physically separated. This feature is useful when a lectin contacts separate branches of a glycan. B, Motif families. The tree shows the relationships between the groups of glycans with the indicated motifs, using a simulated analysis. The first split represents primary motifs (A and B) to which a protein binds. Motif B can be split into sub-motifs that represent fine specificities. C, The simulated data show the ranges of lectin binding to the glycans in each of the motif groups. For example, the glycans in group B contain motif B but not motif A. The B₁-B₄ sub-motifs define fine-specificities with differing ranges of binding, potentially explaining the broad range of the parent motif B.