Did You Know?
Proteoglycans were previously known as mucopolysaccharides.
The extracellular matrix (ECM) is a matrix secreted by the cells in a tissue, that provides structural and biochemical support to all the cells of that tissue. It is a complex mix of various biological molecules and fibers. The biomolecules are of three types - glycosaminoglycans, proteoglycans, and glycoproteins. All three differ from each other based on structure, function, and location. However, glycosaminoglycans can be included under the umbrella of proteoglycans
, since the aggregation of multiple glycosaminoglycans around a protein core forms a proteoglycan molecule.
Proteoglycans are also considered as a special subset of glycoproteins but are mentioned as a distinct entity. This is because, despite both molecules having a protein core (polypeptide chain), the molecules that aggregate on those cores are dissimilar. This dissimilarity leads to a difference in structure, function, and in turn, to a difference in location. These and other such differences between the two molecules have been listed and explained below.
Glycoproteins Vs. Proteoglycans
★ Oligosaccharide (carbohydrate) chains are covalently attached to a polypeptide side chain.
★ Glycosaminoglycan (GAG) chain(s) are attached to a polypeptide side chain.
Nature of Chains
★ Oligosaccharide chains are short, branched, and may or may not be negatively charged.
★ Glycosaminoglycan chains are long, linearized, and negatively charged because of the presence of sulfate and uronic acid functional groups.
★ 10 - 15% by weight
★ 50 - 60% by weight
★ Broadly categorized as N-linked and O-linked saccharides.
★ Classification depends on the nature of the GAG chains.
★ Glycoproteins are found on the cell surface with the carbohydrate chains placed outside the cell.
★ Proteoglycans are found in the connective tissues.
★ Glycoproteins act as integral membrane proteins, and play a role in cell-cell recognition and signaling.
★ Proteoglycans provide structural support and mechanical strength to the ECM, play a role in the modulation of cell growth processes, and provide padding in joints.
★ ABO blood group antigens
★ Hormones like follicle stimulating hormone(FSH)
Studying the differences between these two molecules of the ECM
allows us to gain an understanding of the way these molecules function and interact with each other to ensure smooth functioning of various cellular and tissue processes.