title: Structure of a conserved dimerization domain within the F-box protein Fbxo7 and the PI31 proteasome inhibitor.
abstract: F-box proteins are the substrate-recognition components of the Skp1-Cul1-F box protein (SCF) E3 ubiquitin ligases. Here we report a structural relationship between Fbxo7, a component of the SCF(Fbxo7) E3 ligase, and the proteasome inhibitor PI31. SCF(Fbxo7) is known to catalyze the ubiquitination of hepatoma-up-regulated protein (HURP) and the inhibitor of apoptosis (IAP) protein but also functions as an activator of cyclin D-Cdk6 complexes. We identify PI31 as an Fbxo7.Skp1 binding partner and show that this interaction requires an N-terminal domain present in both proteins that we term the FP (Fbxo7/PI31) domain. The crystal structure of the PI31 FP domain reveals a novel alpha/beta-fold. Biophysical and mutational analyses are used to map regions of the PI31 FP domain mediating homodimerization and required for heterodimerization with Fbxo7.Skp1. Equivalent mutations in Fbxo7 ablate interaction with PI31 and also block Fbxo7 homodimerization. Knockdown of Fbxo7 does not affect PI31 levels arguing against PI31 being a substrate for SCF(Fbxo7). We present a model for FP domain-mediated dimerization of SCF(Fbxo7) and PI31.
authors.affiliation: Structural Biology Laboratory, London Research Institute, Cancer Research UK, 44 Lincoln's Inn Fields, London WC2A 3PX, United Kingdom.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Kirk
authors.forename: Heike
authors.initials: H
authors.lastname: Laman
authors.forename: Phillip P
authors.initials: PP
authors.lastname: Knowles
authors.forename: Judith
authors.initials: J
authors.lastname: Murray-Rust
authors.forename: Mikhail
authors.initials: M
authors.lastname: Lomonosov
authors.forename: El Kahina
authors.initials: el K
authors.lastname: Meziane
authors.forename: Neil Q
authors.initials: NQ
authors.lastname: McDonald
mesh_terms: D000595:Amino Acid Sequence; D045744:Cell Line, Tumor; D019281:Dimerization; D044783:F-Box Proteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D046988:Proteasome Endopeptidase Complex; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D044783:F-Box Proteins; C489149:FBXO7 protein, human; C121623:PSMF1 protein, human; D011506:Proteins; D046988:Proteasome Endopeptidase Complex