Fibulin-1 Is a Ligand for the C-type Lectin Domains of Aggrecan and Versican

Anders Aspberg,Susanne Adam,Günter Kostka,Rupert Timpl,Dick Heinegård

doi:10.1074/jbc.274.29.20444

Anders Aspberg, Susanne Adam + Show 3 more

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https://doi.org/10.1074/jbc.274.29.20444

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Abstract

The aggregating proteoglycans (aggrecan, versican, neurocan, and brevican) are important components of many extracellular matrices. Their N-terminal globular domain binds to hyaluronan, but the function of their C-terminal region containing a C-type lectin domain is less clear. We now report that a 90-kDa protein copurifies with recombinant lectin domains from aggrecan and versican, but not from the brain-specific neurocan and brevican. Amino acid sequencing of tryptic peptides from this protein identified it as fibulin-1. This extracellular matrix glycoprotein is strongly expressed in tissues where versican is expressed (blood vessels, skin, and developing heart), and also expressed in developing cartilage and bone. It is thus likely to interact with these proteoglycans in vivo. Surface plasmon resonance measurements confirmed that aggrecan and versican lectin domains bind fibulin-1, whereas brevican and neurocan do not. As expected for a C-type lectin, the interactions with fibulin-1 are Ca2+-dependent, with KD values in the low nanomolar range. Using various deletion mutants, the binding site for aggrecan and versican lectin domains was mapped to the epidermal growth factor-like repeats in domain II of fibulin-1. No difference in affinity was found for deglycosylated fibulin-1, indicating that the proteoglycan C-type lectin domains bind to the protein part of fibulin-1.

Highlights

The lectican family of large aggregating proteoglycans consists of versican, aggrecan, neurocan, and brevican [1]
Fibulin-1 Copurifies with Recombinant Versican and Aggrecan Lectin Domains—We observed that a 90-kDa protein copurified with select rCLD proteins in Ni-NTA-agarose chromatography from conditioned medium of transfected human embryonal kidney 293-EBNA cells (Fig. 1)
In this paper we demonstrate that fibulin-1 is a high affinity ligand for the C-type lectin domains of the proteoglycans versican and aggrecan

Summary

Introduction

The lectican family of large aggregating proteoglycans consists of versican, aggrecan, neurocan, and brevican [1] Their core proteins are organized with a central, extended, glycosaminoglycan-carrying part of variable length, flanked by globular domains [2,3,4,5,6]. We have recently shown that the C-terminal globular domain functions as a binding domain, in that it binds the brain-specific extracellular matrix protein tenascin-R [11, 12]. All these proteoglycans are expressed in the brain [1, 13]. The striking overlap in the expression pattern of fibulin and those of versican and aggrecan, suggests that this interaction is of physiological importance

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