Question

What are lectins?what are their functions? What are different types of sugars present? How do they determine to which sugar they want to bind to?

(Make sure it’s brief)

Answer 1

Lectins are carbohydrate-binding proteins. They are mostly of plant origin and are macromolecules which are highly specific for sugar moieties of other molecules. By binding to the sugar they cause agglutination of particular cell types.

Since lectins are a type of protein that can bind to cell membranes and are sugar-binding by nature, they become the 'glyco' portion of the glycoconjugates on the membranes. Thus, they offer a way for molecules to stick together without getting the immune system involved, which can influence cell-cell interaction.

The lectin pathway starts with mannose-binding lectin [MBL] or ficolin binding to certain sugars. The MBL binds to mannose, glucose or other sugars with 3- and 4-OH groups. Lectins are capable of binding to many types of carbohydrates, such as--

* Monosaccharides and disaccharides have shallow grooves to which lectins bind and this is why the bond affinity is low.

* The shape of the binding sites in carbohydrate is also a factor in its bondage to lectins. For example, galectin-1 binds to the pentasaccharide - ganglioside GM 1 by two branches.

* Core substitutions in N- glycans are added to specific positions on the carbohydrate. These substitutions prominently affect the properties of the glycans. These substitutions, resulting in changes of certain parts of carbohydrates, act as molecular switches governing the shape of glycans.

* Affinity of lectins for carbohydrates showing branches is also noticed. The increase in affinity is determined by the type of branching.