CTLDcontaining

CTLD-containing refers to proteins that harbor a C-type lectin-like domain (CTLD), a conserved carbohydrate-binding fold found in a wide range of organisms. The CTLD is typically about 110 amino acids and often requires calcium for carbohydrate recognition, though variations exist and some CTLD-bearing proteins function in calcium-independent ways.

These proteins can be secreted or membrane-bound, and they show diverse domain architectures. Collectins such as mannose-binding lectin (MBL) and the surfactant proteins SP-A and SP-D are collagen-containing CTLD proteins that form oligomeric structures to bind microbial carbohydrates and can initiate the lectin pathway of complement. Other CTLD-containing proteins act as receptors on immune cells, including DC-SIGN (CD209), Dectin-1 (CLEC7A), and Langerin (CD207), which recognize pathogens and mediate phagocytosis or signaling.

CTLD-containing proteins are widespread in animals and are also found in other kingdoms, reflecting deep evolutionary roots. They contribute to innate immunity, pathogen recognition, cell adhesion, and endocytosis, and several have been explored as therapeutic targets or biomarkers in infections, inflammation, and cancer. The term CTLD-containing is a broad annotation for a large and diverse set of molecules united by the presence of the C-type lectin-like domain, rather than by a single function or family.