They are major components of the extracellular matrix or ground substance.

GAGs carry sulfate and carboxyl groups which give them a negative charge and have special ability to bind large amounts of water, thereby producing a gel-like matrix which functions as a cushion against mechanical shocks.

They lubricate joints both at the surface of cartilage and in synovial fluid.

The viscous lubricating properties of mucus secretions are also due to the presence of glycosaminoglycans