Aggrecan

Aggrecan, also known as cartilage-specific proteoglycan core protein (CSPCP) or chondroitin sulfate proteoglycan 1, is a protein that in humans is encoded by the ACAN gene. This gene is a member of the lectican (chondroitin sulfate proteoglycan) family. The encoded protein is an integral part of the extracellular matrix in cartilagenous tissue and it withstands compression in cartilage.

Aggrecan is a proteoglycan, or a protein modified with large carbohydrates; the human form of the protein is 2316 amino acids long and can be expressed in multiple isoforms due to alternative splicing.

Structure

Aggrecan is a high molecular weight (1x10⁶ < M < 3x10⁶) proteoglycan. It exhibits a bottlebrush structure, in which chondroitin sulfate and keratan sulfate glycosaminoglycan (GAG) chains are attached to an extended protein core.

Aggrecan has a molecular mass >2,500 kDa. The core protein (210–250 kDa) has 100–150 GAG chains attached to it.

Aggrecan consists of two globular structural domains (G1 and G2) at the N-terminal end and one globular domain (G3) at the C-terminal end, separated by a large extended domain (CS) heavily modified with GAGs. (N-G1-G2-CS-G3-C) The two main modifier moieties are themselves arranged into distinct regions, a chondroitin sulfate and a keratan sulfate region.