Identification of versican as an isolectin B4‐binding glycoprotein from mammalian spinal cord tissue

Abstract

Nociceptors are specialized nerve fibers that transmit noxious pain stimuli to the dorsal horn of the spinal cord. A subset of nociceptors, the nonpeptidergic C‐fibers, is characterized by its reactivity for the plant isolectin B4 (IB4) from Griffonia simplicifolia. The molecular nature of the IB4‐reactive glycoconjugate, although used as a neuroanatomical marker for more than a decade, has remained unknown. We here present data which strongly suggest that a splice variant of the extracellular matrix proteoglycan versican is the IB4‐reactive glycoconjugate associated with these nociceptors. We isolated (by subcellular fractionation and IB4 affinity chromatography) a glycoconjugate from porcine spinal cord tissue that migrated in SDS/PAGE as a single distinct protein band at an apparent molecular mass of > 250 kDa. By using MALDI‐TOF/TOF MS, we identified this glycoconjugate unambiguously as a V2‐like variant of versican. Moreover, we demonstrate that the IB4‐reactive glycoconjugate and the versican variant can be co‐released from spinal cord membranes by hyaluronidase, and that the IB4‐reactive glycoconjugate and the versican variant can be co‐precipitated by an anti‐versican immunoglobulin and perfectly co‐migrate in SDS/PAGE. Our findings shed new light on the role of the extracellular matrix, which is thought to be involved in plastic changes underlying pain‐related phenomena such as hyperalgesia and allodynia.