Collectin

Collectin is a type of protein that plays a crucial role in the immune system. It is part of the C-type lectin family, which is involved in the body's defense against pathogens. Collectins are found in the blood plasma and on the surfaces of certain cells, where they bind to specific carbohydrates on the surfaces of microorganisms, leading to their destruction.

Structure

Collectins are composed of multiple polypeptide chains, each of which has a collagen-like region and a carbohydrate recognition domain (CRD). The CRD allows the collectin to bind to specific carbohydrates on the surfaces of microorganisms.

Function

Collectins play a key role in the immune system's defense against pathogens. They bind to specific carbohydrates on the surfaces of microorganisms, marking them for destruction by the immune system. This process is known as opsonization. In addition to their role in immune defense, collectins also play a role in inflammation and apoptosis (cell death).

Types

There are several types of collectins, including Mannose-binding lectin (MBL), Surfactant protein A (SP-A), and Surfactant protein D (SP-D). Each of these has a slightly different structure and function.

Mannose-binding lectin

MBL binds to mannose residues on the surfaces of many types of pathogens, including bacteria, viruses, and fungi. It plays a key role in the body's defense against these organisms.

Surfactant proteins A and D

SP-A and SP-D are found in the lungs, where they play a key role in the body's defense against respiratory pathogens. They bind to specific carbohydrates on the surfaces of these organisms, marking them for destruction by the immune system.

Clinical significance

Deficiencies in collectins can lead to increased susceptibility to infections. For example, individuals with low levels of MBL are more susceptible to certain types of bacterial and fungal infections. In addition, mutations in the genes that encode collectins can lead to diseases such as congenital disorders of glycosylation.

See also

• C-type lectin
• Immune system
• Opsonization
• Mannose-binding lectin
• Surfactant protein A
• Surfactant protein D