Proteoglycans vs Glycoproteins
Glycoproteins and proteoglycams are two types of molecules that contain both proteins and carbohydrate units. The carbohydrate units are bound covalently to proteins molecules, varying in size from monosaccharides to polysaccharides.
Proteins to which carbohydrates are covalently bound through glycosidic bonds are called glycoproteins. Glycoproteins are commonly found in the body and are an important part of the membranes and Golgi apparatus in cells. In addition, they also serve as the cellular recognition molecules such as receptors, adhesion molecules, etc. The two types of glycosylation are; N-glycosylation and O-glycosylation. The principle carbohydrates in human glycoproteins are glucose, mannose, fucose, acetylgalactosamine, acetylglucosamine, acetyleuraminic acid, and xylose. Some hormones are also considered as glycoproteins, for example; FSH, LH, TSH, EPO etc.
Proteoglycans composed of a protein core with one or more covalently attached glycosaminoglycan (GAG) chains. Proteoglycans are found in connective tissues, and they contribute to the organization and the physical properties of the extracellular matrix. Based on the nature of the glycosaminoglycan chain, proteoglycans can be divided into several categories, including; chondroitin sulfate/ demean sulfate, heparin sulfate, chondroitin sulfate, and keratan sulfate. Proteoglycans can also be divided based on their size as small and large proteoglycans.
What is the difference between Glycoproteins and Proteoglycans?
• Proteoglycans have long unbranched chains with disaccharide units as repeating structures. In contrast, glycoproteins have short highly branched glycan chains with no repeating unit.
• The carbohydrate content of proteoglycans is about 10 – 15%, whereas that of glycoproteins is 50 – 60% by weight.
• Proteoglycans are considered as a subclass of glycoproteins.
• Carbohydrate chains of proteoglycans are negatively charged due to the presence of sulfate and uronic acid groups, whereas that of glycoproteins may or may not be negatively charged.
• Glycoproteins are found mainly in cellular membrane of cells while proteoglycans are found mainly in connective tissues.
• Proteoglycans are important in modulation of cellular development processes, whereas glycoproteins function in cellular recognition.