Structural basis for the sheddase function of human meprin β metalloproteinase at the plasma membrane

Abstract

Ectodomain shedding at the cell surface is a major mechanism to regulate the extracellular and circulatory concentration or the activities of signaling proteins at the plasma membrane. Human meprin β is a 145-kDa disulfide-linked homodimeric multidomain type-I membrane metallopeptidase that sheds membrane-bound cytokines and growth factors, thereby contributing to inflammatory diseases, angiogenesis, and tumor progression. In addition, it cleaves amyloid precursor protein (APP) at the β-secretase site, giving rise to amyloidogenic peptides. We have solved the X-ray crystal structure of a major fragment of the meprin β ectoprotein, the first of a multidomain oligomeric transmembrane sheddase, and of its zymogen. The meprin β dimer displays a compact shape, whose catalytic domain undergoes major rearrangement upon activation, and reveals an exosite and a sugar-rich channel, both of which possibly engage in substrate binding. A plausible structure-derived working mechanism suggests that substrates such as APP are shed close to the plasma membrane surface following an "N-like" chain trace. P hysiological processes in the extracellular milieu and the circulation require finely tuned concentrations of signal molecules such as cytokines, growth factors, receptors, adhesion molecules, and peptidases. Many of these proteins are synthesized as type-I membrane protein variants or precursors consisting of a glycosylated N-terminal ectoprotein, a transmembrane helix, and a Cterminal cytosolic tail. Their localization at the cell surface restricts their field of action to autocrine or juxtacrine processes. However, to act at a distance in paracrine, synaptic, or endocrine events, they have to be released from the plasma membrane into the extracellular space as soluble factors through "protein ectodomain shedding" (1, 2). This entails limited proteolysis and is a major posttranslational regulation mechanism that affects 2-4% of the proteins on the cell surface, occurs at or near the plasma membrane (3), and apparently follows a common release mechanism (2). It may also proteolytically inactivate proteins to terminate their function on the cell surface (4). Peptidases engaged in such processing are "sheddases" and the most studied transmembrane sheddases are members of the adamalysin/ADAMs (4, 5) and matrix-metalloproteinase (MMP) (6) families within the metzincin clan of metallopeptidases (MPs) (7-9). These include ADAM

The Metalloprotease Meprin β Is an Alternative β-Secretase of APP

“…Since BACE-1 is not capable in directly generating this peptide, a suggested model for the emergence of N-terminal truncation is the subsequent cleavage of the N-terminus of BACE generated Aβ1-x by either Aβ degrading enzymes like insulin-degrading enzymes (IDE) or neprilysin or the aminopeptidase A (APA) (Arai et al, 1999; Wiltfang et al, 2001; Wang et al, 2006). A candidate directly generating N-terminally truncated Aβ independent of BACE-1 is the metalloprotease meprin β. Meprin β is a multi-domain type I transmembrane protein, member of the astacin family of zinc-endopeptidases that is predominantly present as a dimer at the cell surface (Arolas et al, 2012; Figure 2). In 2011 meprin β was introduced as an alternative enzyme involved in APP processing (Jefferson et al, 2011).…”

Ectodomain shedding of CD99 within highly conserved regions is mediated by the metalloprotease meprin β and promotes transendothelial cell migration

“…Meprin b, a multidomain type I transmembrane metalloprotease, is an initiator of RIP, and structural studies revealed dimeric formation of the protease with the active site in proximity to the cell surface (2)(3)(4). In addition, meprin b can be shed from the cell surface by ADAM10/ 17, resulting in a soluble active protease, which for instance is important for mucus detachment in the small intestine (5).…”

Crystal Structure of the Neuropilin-1 MAM Domain: Completing the Neuropilin-1 Ectodomain Picture

“…Therefore the observed dimer in the asymmetric unit is possibly a crystallographic artifact of no physiological relevance. In contrast to the meprin MAM domain (Arolas et al., 2012), which contains five cysteine residues in the MAM domain of NRP1, no intermolecular disulfide bond can be formed as the four cysteine side chains present form intramolecular disulfide bonds, thus eliminating cysteine-dependent oligomerization as a mechanism of NRP1 self-association. However, it has recently been postulated that the integrity of the intramolecular disulfide bonds might regulate NRP oligomerization (Barton et al., 2015).…”

“…Overlaying the MAM domain structure from RPTPmu (PDB: 2C9A, residues 1–187, 25% sequence identity to NRP1) (Aricescu et al., 2006) and meprin (PDB: 4GWM, residues 257–428, 29% sequence identity to NRP1) (Arolas et al., 2012) to that of NRP1 gives an RMSD for Cα atoms of 1.6 Å and 1.7 Å, respectively (Figure 3B). The β strands overlap very well while the flexible loops are the main source of variation between the three structures.…”