Decorin is a Zn²⁺ metalloprotein

Decorin is ubiquitously distributed in the extracellular matrix of mammals and a member of the proteoglycan family characterized by a core protein dominated by leucine-rich repeat motifs. We show here that decorin extracted from bovine tissues under denaturing conditions or produced in recombinant 'native' form by cultured mammalian cells has a high affinity for Zn²⁺ as demonstrated by equilibrium dialyses. The Zn²⁺-binding sites are localized to the N-terminal domain of the core protein that contains 4 Cys residues in a spacing reminiscent of a zinc finger. A recombinant 41-amino acid long peptide representing the N-terminal domain of decorin has full Zn²⁺ binding activity and binds two Zn²⁺ ions with an average K(D) of 3 x 10^-7 M. Binding of Zn²⁺ to this peptide results in a change in secondary structure as shown by circular dichroism spectroscopy. Biglycan, a proteoglycan that is structurally closely related to decorin contains a similar high affinity Zn²⁺-binding segment, whereas the structurally more distantly related proteoglycans, epiphycan and osteoglycin, do not bind Zn²⁺ with high affinity.