title: Crystal structure of a dodecameric tetrahedral-shaped aminopeptidase.
abstract: Protein turnover is an essential process in living cells. The degradation of cytosolic polypeptides is mainly carried out by the proteasome, resulting in 7-9-amino acid long peptides. Further degradation is usually carried out by energy-independent proteases like the tricorn protease from Thermoplasma acidophilum. Recently, a novel tetrahedral-shaped dodecameric 480-kDa aminopeptidase complex (TET) has been described in Haloarcula marismortui that differs from the known ring- or barrel-shaped self-compartmentalizing proteases. This complex is capable of degrading most peptides down to amino acids. We present here the crystal structure of the tetrahedral aminopeptidase homolog FrvX from Pyrococcus horikoshii. The monomer has a typical clan MH fold, as found for example in Aeromonas proteolytica aminopeptidase, containing a dinuclear zinc active center. The quaternary structure is built by dimers with a length of 100 A that form the edges of the tetrahedron. All 12 active sites are located on the inside of the tetrahedron. Substrate access is granted by pores with a maximal diameter of 10 A, allowing only small peptides and unfolded proteins access to the active site.
authors.affiliation: Departement für Chemie und Biochemie, University of Berne, Freiestrasse 3, CH-3012 Bern, Switzerland.
authors.forename: Santina
authors.initials: S
authors.lastname: Russo
authors.forename: Ulrich
authors.initials: U
authors.lastname: Baumann
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000626:Aminopeptidases / Q000737:chemistry*; D019843:Archaeal Proteins / Q000737:chemistry; D001665:Binding Sites; D003600:Cytosol / Q000201:enzymology; D019614:Haloarcula marismortui / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D043902:Pyrococcus horikoshii / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D015032:Zinc / Q000737:chemistry
chemical_list: D000596:Amino Acids; D019843:Archaeal Proteins; D000626:Aminopeptidases; D015032:Zinc