Association of Sonic Hedgehog with the extracellular matrix requires its zinc-coordination center

Sonic Hedgehog (Shh) has a catalytic cleft characteristic for zinc metallopeptidases and has significant sequence similarities with some bacterial peptidoglycan metallopeptidases defining a subgroup within the M15A family that, besides having the characteristic zinc coordination motif, can bind two calcium ions. Extracellular matrix (ECM) components in animals include heparan-sulfate proteoglycans, which are analogs of bacterial peptidoglycan and are involved in the extracellular distribution of Shh.

We found that the zinc-coordination center of Shh is required for its association to the ECM as well as for non-cell autonomous signaling. Association with the ECM requires the presence of at least 0.1 μM zinc and is prevented by mutations affecting critical conserved catalytical residues. Consistent with the presence of a conserved calcium binding domain, we find that extracellular calcium inhibits ECM association of Shh.

Our results indicate that the putative intrinsic peptidase activity of Shh is required for non-cell autonomous signaling, possibly by enzymatically altering ECM characteristics.