Glycosaminoglycans (GAGs)

 

Introduction

Even though saccharides commonly are known mostly as sweeteners (sucrose), source of food (carbohydrates) and as strong functional materials like wood (cellulose), there are many other important types of carbohydrates in nature.  

One of the most prominent and biologically important  group of saccharides are the so called Glycosaminoglycans (GAGs). They are found in the body in connective tissues, on cell surfaces and in the blood stream.  As such they are involved in many essential biological processes and bind to a large number of different proteins.

 

 

Types

All GAGs have some similar features in the sense that they  are unbranched polysaccharides consisting of a repeating disaccharide unit. Most glycosaminoglycans have different levels of sulfate groups attached. This makes GAGs highly negatively charged as the sulfates are not protonated under physiological conditions. There are 6 major types of GAGs: Chondroitin sulphate, Dermatan sulphate, Keratan sulphate, Heparin, Heparan sulphate and Hyaluronan (see Table 1).

 

 

Table 1:  Glycosaminoglycans and their function.

GAG

Function

Use

 

Potential new

treatments

Structure

Heparin

Anticoagulation, growth factor binding,

 

 

IdoA(2S)-a(1-4)-GlcN(NS,6S)-a(1-4)

Heparan sulphate

 

 

 

GlcA(IdoA2S)-b(1-4)-GlcN(NAc or NS and/or 6S, 3S)-a(1-4)

Chondroitin sulphate

 

 

 

GlcA(2S)b(1-3)-GalNAc(4S and/ or 4S,6S)b(1-4)

Dermatan sulphate

Anticoagulation, wound repair, cellular proliferation

 

Cancer, antibacterial, antiviral

IdoA(2S)a(1-3)-GalNAc(4S and/ or 4S,6S)b(1-4)

Keratan sulphate

 

 

 

Gal(6S)b(1-4)-GlcNAc(6S and/or NS)b(1-3)

Hyaluronan

 

 

 

GlcA-b(1-3)-GlcN-b(1-4)

 

 

Structure

Glycosaminoglycans are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit (except for keratan) consists of an amino sugar (N-acetylglucosamine or N-acetylgalactosamine) along with a uronic sugar (glucuronic acid or iduronic acid) or galactose. Most glycosaminoglycans (except Hyaluronan) have different degrees of sulfate groups attached. This makes GAGs highly negatively charged as the sulfates are not protonated under physiological conditions. It also means that an astronomical number of sulfate patterns are possible as GAGs often are found as heterogenous mixtures (in particular Heparan Sulphate). They are highly polar and attract water and therefore are useful to the body as a lubricant or as a shock absorber.