title: Scaffolding in the Spliceosome via Single α Helices.
abstract: The spliceosomal B complex-specific protein Prp38 forms a complex with the intrinsically unstructured proteins MFAP1 and Snu23. Our binding and crystal structure analyses show that MFAP1 and Snu23 contact Prp38 via ER/K motif-stabilized single α helices, which have previously been recognized only as rigid connectors or force springs between protein domains. A variant of the Prp38-binding single α helix of MFAP1, in which ER/K motifs not involved in Prp38 binding were mutated, was less α-helical in isolation and showed a reduced Prp38 affinity, with opposing tendencies in interaction enthalpy and entropy. Our results indicate that the strengths of single α helix-based interactions can be tuned by the degree of helix stabilization in the unbound state. MFAP1, Snu23, and several other spliceosomal proteins contain multiple regions that likely form single α helices via which they might tether several binding partners and act as intermittent scaffolds that facilitate remodeling steps during assembly of an active spliceosome.
authors: Laboratory of Structural Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany.
authors: Alexander K C
authors: AKC
authors: Ulrich
authors: Laboratory of Structural Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany.
authors: Martin
authors: M
authors: Seeger
authors: Laboratory of Structural Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany.
authors: Tonio
authors: T
authors: Schütze
authors: Laboratory of Structural Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany.
authors: Natascha
authors: N
authors: Bartlick
authors: Laboratory of Structural Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany; Helmholtz-Zentrum Berlin für Materialien und Energie, Macromolecular Crystallography, Albert-Einstein-Straße 15, 12489 Berlin, Germany. Electronic address: mwahl@zedat.fu-berlin.de.
authors: Markus C
authors: MC
authors: Wahl
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D003285:Contractile Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D016326:Extracellular Matrix Proteins / Q000737:chemistry*; D006801:Humans; D008958:Models, Molecular; D011485:Protein Binding; D017433:Protein Structure, Secondary; D000072260:RNA Splicing Factors / Q000737:chemistry*; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry*; D017381:Spliceosomes / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D003285:Contractile Proteins; D016326:Extracellular Matrix Proteins; D000072260:RNA Splicing Factors; D017411:Ribonucleoproteins, Small Nuclear; C016598:microfibrillar protein
keywords: B-specific proteins; ER/K motif; entropy-enthalpy compensation; intrinsically disordered protein; pre-mRNA splicing; spliceosome catalytic activation