Sialic acid-binding immunoglobulin-type lectins, perhaps best known as SIGLECs, are surface-level proteins responsible for multiple interactions. They primarily oversee sialic acid binding. Usually, they can be seen on an immune cell’s surface. These proteins are a subcategory of I-type lectins, where there being numerous different types.
These different types oversee and are involved in quite a few functions. Cell surface receptor-ligand interactions will be the main factor in determining exactly what these SIGLECs are used for.
Every SIGLEC has what’s known as an N-terminal V-type immunoglobulin domain. That’s responsible for ensuring adhesion and proper binding with sialic acid. On the protein’s surface, there are C2-type Ig domains, which extend beyond the protein itself. These don’t have any binding qualities, however.
The proteins also include Immunoreceptor tyrosine-based inhibitory motifs, with these contained in their cytosolic region.
A SIGLEC’s primary function is to bind sialic acid. That interaction can be seen in multiple processes, including cell signalling and adhesion. They are, however, limited to cell distribution, making their versatility and overall use relatively restricted.
Because most of these proteins are short, their activity is restricted to the surface of cells. That also means that they can’t bind to cells other than sialic acid. That’s primarily due to mammalian cells, which typically include sialic acid-containing glycans.
As a result, the protein can only bind to the surface of these cells without being able to penetrate deeper. There are some minor exceptions, however. The most notable is Sialoadhesin. This chemical has a long, extended protein, which can aid with further interactions with the protein.