CD22 or cluster of differentiation

Cluster of differentiation

The cluster of differentiation is a protocol used for the identification and investigation of cell surface molecules present on white blood cells, providing targets for immunophenotyping of cells...

-22, is a molecule belonging to the SIGLEC

SIGLEC

Siglecs, short for sialic acid binding Ig-like lectins are cell surface receptors and members of the immunoglobulin superfamily that recognize sugars. Their ability to recognize carbohydrates using an immunoglobulin domain places them in the group of I-type lectins...

 family of lectin

Lectin

Lectins are sugar-binding proteins that are highly specific for their sugar moieties. They play a role in biological recognition phenomena involving cells and proteins. For example, some viruses use lectins to attach themselves to the cells of the host organism during infection...

s. It is found on the surface of mature B cells and to a lesser extent on some immature B cells. Generally speaking, CD22 is a regulatory molecule that prevents the overactivation of the immune system and the development of autoimmune diseases.

CD22 is a sugar binding transmembrane protein

Transmembrane protein

A transmembrane protein is a protein that goes from one side of a membrane through to the other side of the membrane. Many TPs function as gateways or "loading docks" to deny or permit the transport of specific substances across the biological membrane, to get into the cell, or out of the cell as...

, which specifically binds sialic acid

Sialic acid

Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a monosaccharide with a nine-carbon backbone. It is also the name for the most common member of this group, N-acetylneuraminic acid...

 with an immunoglobulin (Ig) domain

Immunoglobulin domain

The immunoglobulin domain is a type of protein domain that consists of a 2-layer sandwich of between 7 and 9 antiparallel β-strands arranged in two β-sheets with a Greek key topology....

 located at its N-terminus. The presence of Ig domains makes CD22 a member of the immunoglobulin superfamily

Immunoglobulin superfamily

The immunoglobulin superfamily is a large group of cell surface and soluble proteins that are involved in the recognition, binding, or adhesion processes of cells. Molecules are categorized as members of this superfamily based on shared structural features with immunoglobulins ; they all possess a...

. CD22 functions as an inhibitory receptor for B cell receptor (BCR) signalling.

An immunotoxin, BL22, that targets this receptor is being tested at the NIH.

Interactions

CD22 has been shown to interact

Protein-protein interaction

Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...

 with Grb2

Grb2

Growth factor receptor-bound protein 2 also known as Grb2 is an adaptor protein involved in signal transduction/cell communication. In humans, the GRB2 protein is encoded by the GRB2 gene....

, PTPN6

PTPN6

Tyrosine-protein phosphatase non-receptor type 6 is an enzyme that in humans is encoded by the PTPN6 gene.Also known as Src homology region 2 domain-containing phosphatase-1 .-Interactions:...

, LYN

LYN

Tyrosine-protein kinase Lyn is a protein that in humans is encoded in humans by the LYN gene.Lyn is a member of the Src family of protein tyrosine kinases, which is mainly expressed in hematopoietic cells, in neural tissues liver, and adipose tissue. In various hematopoietic cells, Lyn has emerged...

, SHC1

SHC1

SHC-transforming protein 1 is a protein that in humans is encoded by the SHC1 gene. SHC has been found to be important in the regulation of apoptosis and drug resistance in mammalian cells....

 and INPP5D

INPP5D

Phosphatidylinositol-3,4,5-trisphosphate 5-phosphatase 1 is an enzyme that in humans is encoded by the INPP5D gene.-Interactions:INPP5D has been shown to interact with DOK2, LYN, CD22, Grb2, CRKL, CD31, DOK1 and SHC1.-Further reading:...

.