No abstract

The X-ray crystal structures of two zmc endopeptldases. astacin from crayfish. and adamalysm II from snake venom, reveal a strong overall lopologlcal equivalence and virtually Identical extended HEXXHXXGXXH zinc-binding segments, but m addition a methlomne-containing turn of similar conformatlon (the 'Met-turn'). which forms a hydrophobic basis for the zmc ion and the three ligandmg hlstidine residues. These two features are also present in a similar arrangement m the matrix metalloproteinases (matrixins) and in the large bacterial Serratra proteinase-like peptidases (serralysins).We suggest that these four proteinases represent members of distinct subfamilies which can be grouped together in a family, for which we propose the designation, metzmcins.Astacm; Snake venom metalloproteinase; Matrix metalloprotemase; Thermolysm; Zmc endopeptidase family: Protein crystal structure

Astacin, a digestive zinc-endopeptidase from the crayfish Astacus astacus L., is the prototype for the 'astacin family', which includes mammalian metallo-endopeptidases and developmentally regulated proteins of man, fruitfly, frog and sea urchin. Here we report the X-ray crystal structure of astacin, which reveals a deep active-site cleft, with the zinc at its bottom ligated by three histidines, a water molecule and a more remote tyrosine. The third histidine (His 102) forms part of a consensus sequence, shared not only by the members of the astacin family, but also by otherwise sequentially unrelated proteinases, such as vertebrate collagenases. It may therefore represent the elusive 'third' zinc ligand in these enzymes. The amino terminus of astacin is buried forming an internal salt-bridge with Glu 103, adjacent to His 102. Astacin pro-forms extended at the N terminus, as observed for some 'latent' mammalian astacin homologues, did not exhibit this 'active' conformation, indicating an activation mechanism reminiscent of trypsin-like serine proteinases.

The Ebola virus membrane-associated matrix protein VP40 is thought to be crucial for assembly and budding of virus particles. Here we present the crystal structure of a disk-shaped octameric form of VP40 formed by four antiparallel homodimers of the N-terminal domain. The octamer binds an RNA triribonucleotide containing the sequence 5'-U-G-A-3' through its inner pore surface, and its oligomerization and RNA binding properties are facilitated by two conformational changes when compared to monomeric VP40. The selective RNA interaction stabilizes the ring structure and confers in vitro SDS resistance to octameric VP40. SDS-resistant octameric VP40 is also found in Ebola virus-infected cells, which suggests that VP40 has an additional function in the life cycle of the virus besides promoting virus assembly and budding off the plasma membrane.