a bit about Lectins

You will be using a lectin protein in practical 7, so I thought you might want to know a little about lectins...

Lectins are a group of proteins that bind sugars. Different lectin proteins are able to bind different sugars. For example, Jacalin is a lectin that binds the sugar galactose, and Ulex europaeus agglutinin is a lectin that binds fucose. 

So how does a lectin bind a sugar? And, what makes the binding specific?

Well, different sugars have different structures, for example, look at the following structures of galactose and fucose:

You can see from these diagrams, that whilst galactose and fucose are both 6 membered ring structures, they have a different arrangement of OH groups and fucose has a CH₃ group whereas galactose has a CH₂OH group. Different lectins can recognise these differences because they have binding sites that are very specific to the structure of the sugar they target. The binding site will have a complementary shape to the sugar and it will make weak interactions with the sugar - Van der Waals interactions, hydrogen bonds and electrostatic interactions.

! IMPORTANT ! 

You have to know that a lectin protein has MORE THAN ONE 

sugar binding site

or, put differently, a lectin protein can bind more than one sugar at one time

I have demonstrated this in the following diagram: