C-type lectins are an amazing group of molecules (well all molecules are amazing, LOL), part of the CTLD (C-type lectin-like domain) superfamily of glycoseaminoglycan-binding proteins: touted to be present in all multicellular animals, plants, and fungi and unicellular microorganisms such as a protists, bacteria, and archaea. C-type lectins function in glycoseaminoglycan synthesis, in enzymes, enzyme inhibitors, in coagulation and thrombin, and as esterases, dismutases and topoisomerases and growth factors.  They can be active inside or outside a cell; as cell adhesion molecules, as extracellular matrix proteins, as growth factors and morphogens, as lipid binding proteins, chemokines, lipases, annexins,

A-type lectins (someone will describe someday)

B-lectins (beta-prism lectins)

L-selectins (on lymphocytes —

MBL is a kind of prototype for this family of proteins. (working on this)

Calcium dependence was the key property of the compact carbohydrate recognition domains (CDR). But not all C-type lectins bind carbohydrates. It is clear that the use of the term CRD and c-type lectin domain are often subject to such broad use that confusion arises (review here  ).

Dimers

Trimers

First thing to clarify is whether the term “fold” which is used in many publications is really meant to be “the fold” or a more general description of a property, as in the “folding” plural.  I cannot see how “the fold” would be applicable since there are many folds in any one CRD.