Proteolysis Laboratory, Department of Structural Biology, Molecular Biology Institute of Barcelona Higher Scientific Research Council, Barcelona Science Park, 08028 Barcelona, Spain.
Institut für Molekulare Physiologie, Johannes Gutenberg Universität Mainz, 55128 Mainz, Germany.
Proc Natl Acad Sci U S A. 2021 Apr 6;118(14). doi: 10.1073/pnas.2023839118.
Meprin β (Mβ) 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 Mβ (MβΔC) and FB, which stabilizes the enzyme and inhibits it with subnanomolar affinity. The MβΔC:FB crystal structure reveals a ∼250-kDa, ∼160-Å 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 S to S', but S and S' are spared, which prevents cleavage. Modeling of full-length Mβ reveals an EGF-like domain between MβΔC and the transmembrane segment that likely serves as a hinge to transit between membrane-distal and membrane-proximal conformations for inhibition and catalysis, respectively.
Meprin β (Mβ) 是一种具有多个结构域的 I 型膜金属肽酶，可切割膜锚定的底物，释放其可溶性形式。胎球蛋白-B (FB) 是其唯一已知的内源性蛋白抑制剂。在此，我们分析了 Mβ 胞外结构域 (MβΔC) 与 FB 之间的相互作用，这种相互作用稳定了酶并以亚纳摩尔亲和力抑制了它。MβΔC:FB 晶体结构揭示了一个约 250 kDa、约 160-Å 的多糖基异四聚体颗粒，具有显著的聚糖结构。两个 FB 结构域像楔子一样插入各自的肽酶催化结构域的“CPDCP 主干”和两个发夹中，通过“天冬氨酸开关”机制阻断催化锌离子。独特的是，活性位点裂隙被阻塞在底物 S 到 S' 之间，但 S 和 S' 被保留，从而防止了切割。全长 Mβ的建模表明，MβΔC 和跨膜片段之间存在一个 EGF 样结构域，该结构域可能作为铰链，分别在膜远端和膜近端构象之间转换，以实现抑制和催化。
