The C-terminal region of human plasma fetuin-B is dispensable for the raised-elephant-trunk mechanism of inhibition of astacin metallopeptidases

Human fetuin-B plays a key physiological role in human fertility through its inhibitory action on ovastacin, a member of the astacin family of metallopeptidases. The inhibitor consists of tandem cystatin-like domains (CY1 and CY2), which are connected by a linker containing a "CPDCP-trunk" and followed by a C-terminal region (CTR) void of regular secondary structure. Here, we solved the crystal structure of the complex of the inhibitor with archetypal astacin from crayfish, which is a useful model of human ovastacin. Two hairpins from CY2, the linker, and the tip of the "legumain-binding loop" of CY1 inhibit crayfish astacin following the "raised-elephant-trunk mechanism" recently reported for mouse fetuin-B. This inhibition is exerted by blocking active-site cleft sub-sites upstream and downstream of the catalytic zinc ion, but not those flanking the scissile bond. However, contrary to the mouse complex, which was obtained with fetuin-B nicked at a single site but otherwise intact, most of the CTR was proteolytically removed during crystallization of the human complex. Moreover, the two complexes present in the crystallographic asymmetric unit diverged in the relative arrangement of CY1 and CY2, while the two complexes found for the mouse complex crystal structure were equivalent. Biochemical studies in vitro confirmed the differential cleavage susceptibility of human and mouse fetuin-B in front of crayfish astacin and revealed that the cleaved human inhibitor blocks crayfish astacin and human meprin α and β only slightly less potently than the intact variant. Therefore, the CTR of animal fetuin-B orthologs may have a function in maintaining a particular relative orientation of CY1 and CY2 that nonetheless is dispensable for peptidase inhibition.

The intracellular distribution and secretion of endopeptidases 24.15 (EC 3.4.24.15) and 24.16 (EC 3.4.24.16)

Endopeptidase 24.15 (EC 3.4.24.15; EP24.15) and endopeptidase 24.16 (EC 3.4.24.16; EP24.16) are enzymes involved in general peptide metabolism in mammalian cells and tissues. This review will focus on morphological and biochemical aspects related to the subcellular distribution and secretion of these homologous enzymes in the central nervous system. These are important issues for a better understanding of the functions of EP24.15 and EP24.16 within neuroendocrine systems.

The metalloproteinase MT1-MMP is required for normal development and maintenance of osteocyte processes in bone

The osteocyte is the terminally differentiated state of the osteogenic mesenchymal progenitor immobilized in the bone matrix. Despite their numerical prominence, little is known about osteocytes and their formation. Osteocytes are physically separated in the bone matrix but seemingly compensate for their seclusion from other cells by maintaining an elaborate network of cell processes through which they interact with other osteocytes and bone-lining cells at the periosteal and endosteal surfaces of the bone. This highly organized architecture suggests that osteocytes make an active contribution to the structure and maintenance of their environment rather than passively submitting to random embedding during bone growth or repair. The most abundant matrix protein in the osteocyte environment is type-I collagen and we demonstrate here that, in the mouse, osteocyte phenotype and the formation of osteocyte processes is highly dependent on continuous cleavage of type-I collagen. This collagenolytic activity and formation of osteocyte processes is dependent on matrix metalloproteinase activity. Specifically, a deficiency of membrane type-1 matrix metalloproteinase leads to disruption of collagen cleavage in osteocytes and ultimately to the loss of formation of osteocyte processes. Osteocytogenesis is thus an active invasive process requiring cleavage of collagen for maintenance of the osteocyte phenotype.

Intracellular processing and activation of membrane type 1 matrix metalloprotease depends on its partitioning into lipid domains

The integral membrane type 1 matrix metalloprotease (MT1-MMP) is a pivotal protease in a number of physiological and pathological processes and confers both non-tumorigenic and tumorigenic cell lines with a specific growth advantage in a three-dimensional matrix. Here we show that, in a melanoma cell line, the majority (80%) of MT1-MMP is sorted to detergent-resistant membrane fractions; however, it is only the detergent-soluble fraction (20%) of MT1-MMP that undergoes intracellular processing to the mature form. Also, this processed MT1-MMP is the sole form responsible for ECM degradation in vitro. Finally, furin-dependent processing of MT1-MMP is shown to occur intracellularly after exit from the Golgi apparatus and prior to its arrival at the plasma membrane. It is thus proposed that the association of MT1-MMP with different membrane subdomains might be crucial in the control of its different activities: for instance in cell migration and invasion and other less defined ones such as MT1-MMP-dependent signaling pathways.

Crystal structures, spectroscopic features, and catalytic properties of cobalt(II), copper(II), nickel(II), and mercury(II) derivatives of the zinc endopeptidase astacin. A correlation of structure and proteolytic activity

The catalytic zinc ion of astacin, a prototypical metalloproteinase from crayfish, has been substituted by Co(II), Cu(II), Hg(II), and Ni(II) in order to probe the role of the metal for both catalysis and structure. Compared to Zn(II)-astacin, Co(II)- and Cu(II)-astacin display enzymatic activities of about 140 and 37%, respectively, while Ni(II)- and Hg(II)-astacin are almost inactive. The electron paramagnetic resonance spectrum of Cu(II)-astacin is typical of 5-fold coordinated copper(II), and its intense absorption maxima at 445 and 325 nm are probably due to ligand-metal charge-transfer transitions involving Tyr-149. This residue had been identified previously by x-ray crystallography of the zinc enzyme as a zinc ligand, in addition to three imidazoles and a glutamic acid-bound water molecule. We present now the refined high-resolution x-ray crystal structures of Cu(II)-, Co(II)-, and Ni(II)-astacin, which exhibit a virtually identical protein framework to the previously analyzed structures of Zn(II)-, apo-, and Hg(II)-astacin. In Co(II)- and Cu(II)-astacin, the metal is penta-coordinated similarly to the native zinc enzyme. In the Ni(II) derivative, however, an additional solvent molecule expands the metal coordination sphere to a distorted octahedral ligand geometry, while in Hg(II)-astacin, no ordered solvent molecule at all is observed in the inner coordination sphere of the metal. This indicates a close correlation between catalytic properties and ground-state metal coordination of astacin.

Secondary structure and zinc ligation of human recombinant short-form stromelysin by multidimensional heteronuclear NMR

Stromelysin-1, a member of the matrix metalloendoprotease family, is a zinc protease involved in the degradation of connective tissue in the extracellular matrix. As a step toward determining the structure of this protein, multidimensional heteronuclear NMR experiments have been applied to an inhibited truncated form of human stromelysin-1. Extensive 1H, 13C, and 15N sequential assignments have been obtained with a combination of three- and four-dimensional experiments. On the basis of sequential and short-range NOEs and 13C alpha chemical shifts, two helices have been delineated, spanning residues Asp-111 to Val-127 and Leu-195 to Ser-206. A third helix spanning residues Asp-238 to Gly-247 is characterized by sequential NOEs and 13C alpha chemical shifts, but not short-range NOEs. The lack of the latter NOEs suggests that this helix is either distorted or mobile. Similarly, sequential and interstrand NOEs and 13C alpha chemical shifts characterize a four-stranded beta-sheet with three parallel strands (Arg-100 to Ile-101, Ile-142 to Ala-147, Asp-177 to Asp-181) and one antiparallel strand (Ala-165 to Tyr-168). Two zinc sites have been identified in stromelysin [Salowe et al. (1992) Biochemistry 31, 4535-4540]. The NMR spectral properties, including chemical shift, pH dependence, and proton coupling of the imidazole nitrogens of six histidine residues (151, 166, 179, 201, 205, and 211), invariant in the matrix metalloendoprotease family, suggest that these residues are zinc ligands. NOE data indicate that these histidines form two clusters: one ligates the catalytic zinc (His-201, -205, and -211), and the other ligates a structural zinc (His-151, -166, and -179). Heteronuclear multiple quantum correlated spectra and specific labeling experiments indicate His-151, -179, -201, -205, and -211 are in the N delta 1H tautomer and His-166 is in the N epsilon 2H tautomer.

Assignments for the main-chain nuclear magnetic resonances and delineation of the secondary structure of the catalytic domain of human stromelysin-1 as obtained from triple-resonance 3D NMR experiments

We report the NMR assignments for the main-chain 13C, 15N, and 1H resonances (1HN, 1H alpha, 15N alpha, 13C alpha, 13CO) for the 19.5-kDa catalytic domain of human stromelysin-1, a zinc endoproteinase thought to be involved in pathologic tissue degradation. The assignments were predominantly obtained from triple-resonance three-dimensional NMR experiments using double-labeled (15N/13C) samples. The secondary structure of the molecule was determined from analysis of 3D 15N-resolved NOESY experiments. It was found to consist of a five-stranded mixed beta-sheet with four parallel and one antiparallel strand and three helices. The topological arrangement of the secondary structure elements of stromelysin catalytic domain is remarkably similar to that found for astacin, a Zn proteinase for which the tertiary structure was recently determined from X-ray diffraction data [Bode et al. (1992) Nature 358, 164-167].

Implications of the three-dimensional structure of astacin for the structure and function of the astacin family of zinc-endopeptidases

Astacin, a zinc-endopeptidase from the crayfish Astacus astacus L., represents a structurally distinct group of metalloproteinases termed the 'astacin family'. This protein family includes oligomeric membrane-bound proteins with zinc proteinase domains found in rodent kidneys (meprins A and B) and human small intestine (N-benzoyl-L-tyrosyl-4-aminobenzoate hydrolase). Another branch of this family comprises morphogenetically active proteins, which induce bone formation (human bone morphogenetic protein 1), or which play specific roles during the embryonic development of amphibians, fishes, echinoderms, and insects. The X-ray crystal structure of astacin has recently been solved to a resolution of 0.18 nm [Bode et al. (1992) Nature 358, 164-167]. This structure is different from hitherto known metalloendopeptidase structures and has been used in the present study to analyze the structures of the other members of the astacin protein family. Computer-assisted modelling of the proteolytic domain of the alpha-subunit of meprin A based on the astacin structure is possible if five single and one double residue deletions and three single residue insertions are implied. The proteinase domains of the other astacins can be included in the model-based sequence alignment by introducing additionally three insertions and one deletion. All of these insertions and deletions are observed in loop segments connecting regular secondary structure elements and should leave the overall structure unaltered. The topology of residues forming the zinc-binding active site of astacin corresponds to almost identical arrangements in all other astacins, suggesting that these are likewise metalloproteinases. Based on this similarity, it is proposed that the active-site metal ion of the astacins is penta-coordinated by three histidine residues, a tyrosine residue and a water molecule in a trigonal bipyramidal geometry. Other remarkable common features are a hydrophobic cluster in the N-terminal domain and a conserved, solvent-filled cavity buried in the C-terminal domain. Most interestingly, the amino-termini of all astacins can be modelled to start in a corresponding internal water cavity as seen in the astacin template, where the terminal alanine residue forms a water-linked salt bridge to Glu103, directly adjacent to His102, the third zinc ligand. Therefore, an activation mechanism for the astacins reminiscent of that of the trypsin-like proteinases had been suggested, which now seems to be probable also for the other astacins. Besides these common traits, there are some minor differences which may have important consequences on the function of the astacins.(ABSTRACT TRUNCATED AT 400 WORDS)

Zinc protease of Bacillus subtilis var. amylosacchariticus: construction of a three-dimensional model and comparison with thermolysin

The active site structure of the Zn-containing neutral protease from Bacillus subtilis var. amylosacchariticus (BANP) was predicted by computer-aided modeling on the basis of the three-dimensional structure of thermolysin (TLN). As expected from the high homology in amino acid sequence of the two enzymes, the overall folding of BANP was very similar to that of TLN. Glu144, Tyr158, and His228 of BANP were located near the active site Zn ion, to which three amino acid residues, His143, His147, and Glu167, were coordinated. This model is supported by the previous results that chemical modifications of Tyr158 and photooxidation of His228 of BANP markedly affect the proteolytic activity of the enzyme. Interestingly, BANP was found to be significantly less sensitive to metalloprotease inhibitors such as phosphoramidon and talopeptin. From a comparison of the enzyme-inhibitor complex models between BANP and thermolysin, it is suggested that replacement of Thr129 in TLN by Phe130 in BANP is related to difference in inhibitor sensitivity between BANP and TLN.

The structure of neutral protease from Bacillus cereus at 0.2-nm resolution

The crystal structure of the neutral protease from Bacillus cereus has been refined to an R factor of 17.5% at 0.2-nm resolution. The enzyme, an extracellular metalloendopeptidase, consists of two domains and binds one zinc and four calcium ions. The structure is very similar to that of thermolysin, with which the enzyme shares 73% amino-acid sequence identity. The active-site cleft between the two domains is wider in neutral protease than in thermolysin. This suggests the presence of a flexible hinge region between the two domains, which may assist enzyme action. The high-resolution analysis allows detailed examination of possible causes for the difference in thermostability between neutral protease and thermolysin.