title: Crystal structure of the human U4/U6 small nuclear ribonucleoprotein particle-specific SnuCyp-20, a nuclear cyclophilin.
abstract: The cyclophilin SnuCyp-20 is a specific component of the human U4/U6 small nuclear ribonucleoprotein particle involved in the nuclear splicing of pre-mRNA. It stably associates with the U4/U6-60kD and -90kD proteins, the human orthologues of the Saccharomyces cerevisiae Prp4 and Prp3 splicing factors. We have determined the crystal structure of SnuCyp-20 at 2.0-A resolution by molecular replacement. The structure of SnuCyp-20 closely resembles that of human cyclophilin A (hCypA). In particular, the catalytic centers of SnuCyp-20 and hCypA superimpose perfectly, which is reflected by the observed peptidyl-prolyl-cis/trans-isomerase activity of SnuCyp-20. The surface properties of both proteins, however, differ significantly. Apart from seven additional amino-terminal residues, the insertion of five amino acids in the loop alpha1-beta3 and of one amino acid in the loop alpha2-beta8 changes the conformations of both loops. The enlarged loop alpha1-beta3 is involved in the formation of a wide cleft with predominantly hydrophobic character. We propose that this enlarged loop is required for the interaction with the U4/U6-60kD protein.
authors.affiliation: Institut für Molekularbiologie und Tumorforschung, Universität Marburg, 35037 Marburg, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Reidt
authors.forename: K
authors.initials: K
authors.lastname: Reuter
authors.forename: T
authors.initials: T
authors.lastname: Achsel
authors.forename: D
authors.initials: D
authors.lastname: Ingelfinger
authors.forename: R
authors.initials: R
authors.lastname: Lührmann
authors.forename: R
authors.initials: R
authors.lastname: Ficner
mesh_terms: D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000201:enzymology; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics; D019696:Peptidylprolyl Isomerase / Q000737:chemistry* / Q000235:genetics; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D009687:Nuclear Proteins; D011994:Recombinant Proteins; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D019696:Peptidylprolyl Isomerase