Figure 1.

Collectin structure. (a) Surfactant protein (SP)–A and SP-D are members of the collectin family that function as pattern recognition molecules. Collectins are composed of an N-terminal noncollagenous domain and of a C-type (calcium-dependent) carbohydrate recognition domain (CRD; lectin domain). (b) Structurally, collectins are trimeric polypeptide chains that are assembled into oligomers; SP-A and mannose-binding lectin (MBL) are octodecamers, consisting of six trimeric subunits, and SP-D is a dodecomer, consisting of four trimeric subunits. Models are not drawn to scale. Reprinted by permission from Reference 2.