Isolation of a large aggregating proteoglycan from human brain

Area of Science:

• Neuroscience
• Biochemistry
• Extracellular Matrix Biology

Background:

• The brain extracellular matrix (ECM) contains complex protein-hyaluronate aggregates.
• Glial hyaluronate-binding protein (GHAP) is a known component of these aggregates, interacting with hyaluronate.
• The precise composition and organization of ECM proteoglycans in the central nervous system remain incompletely understood.

Purpose of the Study:

• To isolate and characterize a large proteoglycan from the human brain.
• To determine its relationship to known brain ECM components, particularly GHAP.
• To elucidate the binding properties and anchoring mechanisms of this proteoglycan within the brain ECM.

Main Methods:

• Isolation of proteoglycan using anion-exchange chromatography and gel filtration.
• Characterization via monoclonal antibodies, hyaluronate binding assays, and limited proteolysis.
• Amino-terminal sequencing and immunoblotting to identify the core protein.
• Immunohistochemical localization in bovine spinal cord.

Main Results:

• A 365 kDa chondroitin sulfate proteoglycan was isolated, binding specifically to hyaluronate (HA).
• The proteoglycan's core protein showed sequence identity to human versican.
• Localization in the central nervous system was similar to GHAP, but it was resistant to hyaluronidase digestion.
• Unlike GHAP, which is released by hyaluronidase, this proteoglycan remained associated with the ECM.

Conclusions:

• The brain ECM contains both GHAP and versican, forming protein-hyaluronate aggregates.
• GHAP interacts with hyaluronate for ECM retention.
• The identified versican proteoglycan is anchored independently of hyaluronate, potentially linking cell surfaces to the ECM.