One of two classes of lectin produced by animal cells. The classification of animal lectins into two classes, the other being the C type, was originally proposed by K.Drickamer.
The carbohydrate binding activity of the S type lectins requires their cysteines to have free thiols and does not need divalent cations (c.f. C type lectins). They mostly have molecular masses in the range 14-16 kD and often form dimers and higher oligomers. The carbohydrate recognition domain contains a number of critically conserved amino acids and largely binds to _ galactosides. S type lectins certainly occur as cytoplasmic proteins but the existence of extracellular S type lectins is still a matter of debate.
(18 Nov 1997)