Versican is a large extracellular matrix proteoglycan that is present in a variety of human tissues. It is encoded by the VCAN gene.
Versican is a large chondroitin sulfate proteoglycan with an apparent molecular mass of more than 1000kDa. In 1989, Zimmermann and Ruoslahti cloned and sequenced the core protein of fibroblast chondroitin sulfate proteoglycan. They designated it versican in recognition of its versatile modular structure.
Versican belongs to the lectican protein family, with aggrecan (abundant in cartilage), brevican and neurocan (nervous system proteoglycans) as other members. Versican is also known as chondroitin sulfate proteoglycan core protein 2 or chondroitin sulfate proteoglycan 2 (CSPG2), and PG-M.
Structure
These proteoglycans share a homologous globular N-terminal, C-terminal, and glycosaminoglycan (GAG) binding regions.
The N-terminal (G1) globular domain consists of Ig-like loop and two link modules, and has Hyaluronan (HA) binding properties.
Versican occurs in 5 isoforms : V0, V1, V2, V3, V4. The central domain of versican V0 contains both the GAG-α and GAG-β domains. V1 isoforms has the GAG-β domain, V2 has the GAG-α domain, V3 is void of any GAG attachment domains and V4 has a portion of the GAG-β domain. The GAGs, being composed of repeating disaccharide units, contribute to the negative charge and many other properties of proteoglycans.
The C-terminal (G3) globular domain consists of one or two Epidermal growth factor (EGF) repeats, a C-type lectin domain and complement regulatory protein (CRP)-like domain. The C-terminal domain binds a variety of ligands in ECM which contribute significantly to the functions of lecticans.
Function
The role of versican in cell adhesion, migration, and proliferation has been extensively studied. Versican is often considered an anti-adhesion molecule. Considering the large size (>1000 kDa) and hydration capability of versican, it is possible that the interaction of integrins (large family of cell adhesion molecules) with their cell surface receptors is sterically hindered.
Expression of versican is observed in various adult tissues such as blood vessels, skin, and developing heart. Smooth muscle cells of blood vessels, epithelial cells of skin, and the cells of central and peripheral nervous system are a few examples of cell types that express versican physiologically. Versican is involved in development, guiding embryonic cell migration important in the formation of the heart and outlining the path for neural crest cell migration.
N-terminus
The N-terminal of versican has an important role in maintaining the integrity of the ECM by interacting with hyaluronan. Its interactions with link protein has also been studied.
Glycosaminoglycan binding region
The central domain of Versican is decorated with glycosaminoglycans. The structural and functional diversity of Versican is increased by variations in GAG sulfation patterns and the type of GAG chains bound to the core protein. There is a single versican gene, however alternative splicing of its mRNA produces 4 distinct versican isoforms that differ in their potential number of GAG chains. All isoforms have homologous N-terminal (HA binding) and C-terminal (lectin-like) domains. The central domain of versican V0 contains both the GAG-α and GAG-β domains. V1 isoforms has the GAG-β domain, V2 has the GAG-α domain, and V3 is void of any GAG attachment domains, and only consists of the N-terminal and C-terminal globular domains. It is known that the isoforms are differentially expressed in different tissue types. The biological significance of alternative splicing is yet to be determined.