Crystal Structure of the Human U4/U6 Small Nuclear Ribonucleoproteinparticle-Specificsnucyp-20, a Nuclear CyclophilinReidt, U., Reuter, K., Achsel, T., Ingelfinger, D., Luehrmann, R., Ficner, R.
(2000) J Biol Chem 275: 7439
- PubMed: 10713041
- DOI: https://doi.org/10.1074/jbc.275.11.7439
- Primary Citation of Related Structures:
- PubMed 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.
Institut für Molekularbiologie und Tumorforschung, Universität Marburg, 35037 Marburg, Germany.