title: Structural basis for homodimerization of the Src-associated during mitosis, 68-kDa protein (Sam68) Qua1 domain.
abstract: Sam68 (Src-associated during mitosis, 68 kDa) is a prototypical member of the STAR (signal transducer and activator of RNA) family of RNA-binding proteins. STAR proteins bind mRNA targets and modulate cellular processes such as cell cycle regulation and tissue development in response to extracellular signals. Sam68 has been shown to modulate alternative splicing of the pre-mRNAs of CD44 and Bcl-xL, which are linked to tumor progression and apoptosis. Sam68 and other STAR proteins recognize bipartite RNA sequences and are thought to function as homodimers. However, the structural and functional roles of the self-association are not known. Here, we present the solution structure of the Sam68 Qua1 homodimerization domain. Each monomer consists of two antiparallel alpha-helices connected by a short loop. The two subunits are arranged perpendicular to each other in an unusual four-helix topology. Mutational analysis of Sam68 in vitro and in a cell-based assay revealed that the Qua1 domain and residues within the dimerization interface are essential for alternative splicing of a CD44 minigene. Together, our results indicate that the Qua1 homodimerization domain is required for regulation of alternative splicing by Sam68.
authors.affiliation: Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany.
authors.forename: N Helge
authors.initials: NH
authors.lastname: Meyer
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Tripsianes
authors.forename: Michelle
authors.initials: M
authors.lastname: Vincendeau
authors.forename: Tobias
authors.initials: T
authors.lastname: Madl
authors.forename: Fatiha
authors.initials: F
authors.lastname: Kateb
authors.forename: Ruth
authors.initials: R
authors.lastname: Brack-Werner
authors.forename: Michael
authors.initials: M
authors.lastname: Sattler
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017398:Alternative Splicing / Q000502:physiology; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D018960:Hyaluronan Receptors / Q000096:biosynthesis / Q000235:genetics; D016296:Mutagenesis; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C497483:CD44 protein, human; D004268:DNA-Binding Proteins; D018960:Hyaluronan Receptors; C489559:KHDRBS1 protein, human; D016601:RNA-Binding Proteins