The crystal structure of a 250-kDa heterotetrameric particle explains inhibition of sheddase meprin ß by endogenous fetuin-B

Meprin ss (M ss) is a multidomain type-I membrane metallopeptidase that sheds membrane-anchored substrates, releasing their soluble forms. Fetuin-B (FB) is its only known endogenous protein inhibitor. Herein, we analyzed the interaction between the ectodomain of M ss (M ss Delta C) and FB, which stabilizes the enzyme and inhibits it with subnanomolar affinity. The M ss Delta C:FB crystal structure reveals a similar to 250-kDa, similar to 160-A polyglycosylated heterotetrameric particle with a remarkable glycan structure. Two FB moieties insert like wedges through a CPDCP trunk and two hairpins into the respective peptidase catalytic domains, blocking the catalytic zinc ions through an aspartate switch mechanism. Uniquely, the active site clefts are obstructed from subsites S4 to S10', but S1 and S1' are spared, which prevents cleavage. Modeling of full-length M ss reveals an EGF-like domain between M ss Delta C and the transmembrane segment that likely serves as a hinge to transit between membranedistal and membrane-proximal conformations for inhibition and catalysis, respectively.

Automated summary

The interaction between M ss and FB is analyzed in this study, revealing how FB stabilizes the enzyme and inhibits its activity with high affinity. The crystal structure shows that FB blocks the catalytic activity of M ss through a unique structural mechanism, preventing cleavage of substrates.