Identification and Characterization of a Minimal Functional Splicing Regulatory Protein, PTBP1

Biochemistry. 2020 Dec 22;59(50):4766-4774. doi: 10.1021/acs.biochem.0c00664. Epub 2020 Dec 7.

Abstract

Polypyrimidine tract binding protein 1 (PTBP1) is a well-studied RNA binding protein that serves as an important model for understanding molecular mechanisms underlying alternative splicing regulation. PTBP1 has four RNA binding domains (RBDs) connected via linker regions. Additionally, PTBP1 has an N-terminal unstructured region that contains nuclear import and export sequences. Each RBD can bind to pyrimidine rich elements with high affinity to mediate splicing activity. Studies support a variety of models for how PTBP1 can mediate splicing regulation on target exons. Obtaining a detailed atomic view hinges on determining a crystal structure of PTBP1 bound to a target RNA transcript. Here, we created a minimal functional PTBP1 with deletions in both linker 1 and linker 2 regions and assayed for activity on certain regulated exons, including the c-Src N1 exon. We show that for a subset of PTBP1-regulated exons the linker regions are not necessary for splicing repression activity. Gel mobility shift assays reveal the linker deletion mutant binds with 12-fold higher affinity to a target RNA sequence compared to wild-type PTBP1. A minimal PTBP1 that also contains an N-terminal region deletion binds to a target RNA with an affinity higher than that of wild-type PTBP1. Moreover, this minimal protein oligomerizes readily to form a distinct higher-order complex previously shown to be required for mediating splicing repression. This minimal functional PTBP1 protein can serve as a candidate for future structure studies to understand the mechanism of splicing repression for certain regulated exons.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Alternative Splicing
  • Amino Acid Sequence
  • Animals
  • Calcium Channels, L-Type / genetics
  • Cell Line
  • Electrophoretic Mobility Shift Assay
  • Exons
  • Genes, src
  • Heterogeneous-Nuclear Ribonucleoproteins / chemistry*
  • Heterogeneous-Nuclear Ribonucleoproteins / genetics
  • Heterogeneous-Nuclear Ribonucleoproteins / metabolism*
  • In Vitro Techniques
  • Mice
  • Models, Molecular
  • Polypyrimidine Tract-Binding Protein / chemistry*
  • Polypyrimidine Tract-Binding Protein / genetics
  • Polypyrimidine Tract-Binding Protein / metabolism*
  • Protein Domains
  • RNA / genetics
  • RNA / metabolism
  • RNA Splice Sites
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sequence Deletion

Substances

  • CACNA1C protein, mouse
  • Calcium Channels, L-Type
  • Heterogeneous-Nuclear Ribonucleoproteins
  • Ptbp1 protein, mouse
  • RNA Splice Sites
  • Recombinant Proteins
  • Polypyrimidine Tract-Binding Protein
  • RNA