Nectinepsin: a new extracellular matrix protein of the pexin family. Characterization of a novel cDNA encoding a protein with an RGD cell binding motif

The structure of a haemopexin-fold protein from cow pea (Vigna unguiculata) suggests functional diversity of haemopexins in plants

The haemopexin fold is present in almost all life forms and is utilized for carrying out diverse physiological functions. The structure of CP4, a haemopexin-fold protein from cow pea (Vigna unguiculata), was determined at 2.1 Å resolution. The protein exists as a monomer both in solution and in the crystal. The structure revealed a typical four-bladed β-propeller topology. The protein exhibits 42% sequence similarity to LS-24 from Lathyrus sativus, with substantial differences in the surface-charge distribution and in the oligomeric state. A structure-based sequence analysis of haemopexin-fold proteins of plant and mammalian origin established a sequence signature associated with the haemopexin motif. This signature sequence enabled the identification of other proteins with possible haemopexin-like topology of both plant and animal origin. Although CP4 shares a structural fold with LS-24 and other haemopexins, biochemical studies indicated possible functional differences between CP4 and LS-24. While both of these proteins exhibit spermine-binding potential, CP4 does not bind to haem, unlike LS-24.

Hemopexin domains as multifunctional liganding modules in matrix metalloproteinases and other proteins

The heme-binding hemopexin consists of two, four-bladed propeller domains connected by a linker region. Hemopexin domains are found in different species on the phylogenetic tree and in the human species represented in hemopexin, matrix metalloproteinases (MMPs), vitronectin, and products of the proteoglycan 4 gene. Hemopexin and hemopexin domains of human proteins fulfill functions in activation of MMPs, inhibition of MMPs, dimerization, binding of substrates or ligands, cleavage of substrates, and endocytosis by low-density lipoprotein receptor-related protein-1 (LRP-1; CD91) and LRP-2 (megalin, GP330). Insights into the structures and functions of hemopexin (domains) form the basis for positive or negative interference with the formation of molecular complexes and hence, might be exploited therapeutically in inflammation, cancer, and wound healing.

Changes in expression and localization of hemopexin and its transcripts in injured nervous system: a comparison of central and peripheral tissues

The recent demonstration of hemopexin synthesis in the adult rat sciatic nerve and its accumulation after injury has raised the question of the possible role of this acute phase protein during the process of nerve repair. To gain insight into its function, we have compared the distribution of both hemopexin and its messenger RNA in the peripheral and the central nervous systems. We find that hemopexin is present in all types of peripheral nerves and ganglia, confined to the extracellular matrix and basement membranes of the endoneurium, blood vessels and connective tissues. After injury, hemopexin messenger RNA is overexpressed by Schwann cells, fibroblasts and invading macrophages. The content in hemopexin protein increases in all nerves studied, without changes in localization. Therefore, hemopexin does not appear to be associated with the fate of myelin or with the regeneration of a particular type of nerve fibre. In the central nervous system, hemopexin messenger RNA cannot be detected and the protein is only found in basement membranes of the vascular system (capillaries, meninges and choroid plexus). Furthermore, hemopexin and its messenger RNA remain absent from the distal part of the injured optic nerves. Our results further support the idea that hemopexin plays specific roles during nerve repair, and that it may be associated with the endoneurial extracellular matrix.

A novel matrix metalloproteinase gene (XMMP) encoding vitronectin-like motifs is transiently expressed in Xenopus laevis early embryo development

To study the role of matrix metalloproteinases (MMPs) in early vertebrate development, we cloned cDNAs for six different MMPs from the frog Xenopus laevis embryos at different stages of development and describe here a novel MMP called XMMP. Xenopus XMMP has 604 amino acids including a putative signal peptide of 22 residues. At the carboxyl-terminal end of the propeptide, XMMP has a 37-amino acid-long insertion domain containing a segment that is 38% identical with a rat vitronectin sequence between residues 108-135. Following this domain is an RRKR motif, a putative cleavage site for intracellular activation by furin proteinases. XMMP lacks a proline-rich linker peptide, or hinge region, typically found in other MMPs between the catalytic domain and carboxyl-terminal "hemopexin/vitronectin-like" domain. In XMMP, the carboxyl-terminal domain is composed of four tandem repeats that are 21-33% identical to a sequence (residues 213-264) encoded by vitronectin exon-5. Interestingly, XMMP gene is transiently expressed during Xenopus embryo development. XMMP mRNA of 3.0 kilobase pairs was undetected in the blastula stage embryo, induced in gastrula embryo, expressed in neurula embryo, and then down-regulated in pretailbud embryo. In comparison, other Xenopus MMP genes that we have cloned show a different developmental regulation. In blastula embryo, the only MMP gene expressed was found to be 92-kDa type IV collagenase, which was also expressed in the gastrula, neurula, and pretailbud embryos. Expression of stromelysin-1, stromelysin-3, and two different membrane type-MMPs was first detected in the neurula and pretailbud embryos. These results suggest that MMPs and the novel XMMP reported here play a role in Xenopus early development.