C-type lectin fold <p>Lectins occur in plants, animals, bacteria and viruses. Initially described for their carbohydrate-binding activity [<cite idref="PUB00042634"/>], they are now recognised as a more diverse group of proteins, some of which are involved in protein-protein, protein-lipid or protein-nucleic acid interactions [<cite idref="PUB00042635"/>]. There are at least twelve structural families of lectins, of which C-type (Ca+-dependent) lectins is one. C-type lectins can be further divided into seven subgroups based on additional non-lectin domains and gene structure: (I) hyalectans, (II) asialoglycoprotein receptors, (III) collectins, (IV) selectins, (V) NK group transmembrane receptors, (VI) macrophage mannose receptors, and (VII) simple (single domain) lectins [<cite idref="PUB00042644"/>].</p><p>This entry represents a structural domain found in C-type lectins, as well as in other proteins, including:</p><p> <ul><li>The N-terminal domain of aerolysin [<cite idref="PUB00004166"/>] and the N-terminal domain of the S2/S3 subunit of pertussis toxin [<cite idref="PUB00020076"/>].</li><li>The C-terminal domain of invasin [<cite idref="PUB00018560"/>] and intimin [<cite idref="PUB00006623"/>].</li><li>Link domain, which includes the Link module of TSG-6 [<cite idref="PUB00022318"/>] (a hyaladherin with important roles in inflammation and ovulation) and the hyaluronan binding domain of CD44 (which contains extra N-terminal beta-strand and C-terminal beta-hairpin) [<cite idref="PUB00022805"/>].</li><li>Endostatin [<cite idref="PUB00021244"/>] and the endostatin domain of collagen alpha 1 (XV) [<cite idref="PUB00042646"/>], these domains being decorated with many insertions in the common fold.</li><li>The noncollagenous (NC1) domain of collagen IV, which consists of a duplication of the C-type lectin domain, with segment swapping within and between individual domains [<cite idref="PUB00027036"/>].</li><li>Sulphatase-modifying factors (C-alpha-formyglycine-generating enzyme), where the fold is decorated with many additional structures [<cite idref="PUB00035615"/>, <cite idref="PUB00032580"/>].</li><li>The C-terminal domain of the major tropism determinant (Mtd), where the fold is decorated with many additional structures, and has an overall similarity to the sulphatase modifying factor family but lacking the characteristic disulphide [<cite idref="PUB00038630"/>].</li></ul> </p>