The crystal structure of the non-liganded 14-3-3|[sigma]| protein: insights into determinants of isoform specific ligand binding and dimerization

doi:doi:10.1038/sj.cr.7290290

Cell Research (2005) 15, 219–227. doi:10.1038/sj.cr.7290290

The crystal structure of the non-liganded 14-3-3 protein: insights into determinants of isoform specific ligand binding and dimerization

Anne BENZINGER¹, Grzegorz M POPOWICZ², Joma K JOY², Sudipta MAJUMDAR², Tad A HOLAK² and Heiko HERMEKING¹

¹Molecular Oncology Group, Max-Planck-Institute for Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany
²NMR Group, Max-Planck-Institute for Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany

Correspondence: Heiko HERMEKING, Tel: 011-49-(0)-89-8578-2875 Fax: 011-49-(0)-89-8578-2540 E-mail: herme@biochem.mpg.de

Received 29 March 2005; Revised 31 March 2005; Accepted 1 April 2005.

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Abstract

Seven different, but highly conserved 14-3-3 proteins are involved in diverse signaling pathways in human cells. It is unclear how the 14-3-3 sigma isoform, a transcriptional target of p53, exerts its inhibitory effect on the cell cycle in the presence of other 14-3-3 isoforms, which are constitutively expressed at high levels. In order to identify structural differences between the 14-3-3 isoforms, we solved the crystal structure of the human 14-3-3 sigma protein at a resolution of 2.8 Å and compared it to the known structures of 14-3-3 zeta and 14-3-3 tau . The global architecture of the 14-3-3 sigma fold is similar to the previously determined structures of 14-3-3 zeta and 14-3-3 tau : two 14-3-3 sigma molecules form a cup-shaped dimer. Significant differences between these 14-3-3 isoforms were detected adjacent to the amphipathic groove, which mediates the binding to phosphorylated consensus motifs in 14-3-3-ligands. Another specificity determining region is localized between amino-acids 203 to 215. These differences presumably select for the interaction with specific ligands, which may explain the different biological functions of the respective 14-3-3 isoforms. Furthermore, the two 14-3-3 sigma molecules forming a dimer differ by the spatial position of the ninth helix, which is shifted to the inside of the ligand interaction surface, thus indicating adaptability of this part of the molecule. In addition, 5 non-conserved residues are located at the interface between two 14-3-3 sigma proteins forming a dimer and represent candidate determinants of homo- and hetero-dimerization specificity. The structural differences among the 14-3-3 isoforms described here presumably contribute to isoform-specific interactions and functions.