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Distinct mechanisms govern the phosphorylation of different SR protein splicing factors.

Authors
  • Long, Yunxin1
  • Sou, Weng Hong1
  • Yung, Kristen Wing Yu1
  • Liu, Haizhen1
  • Wan, Stephanie Winn Chee1
  • Li, Qingyun1
  • Zeng, Chuyue1
  • Law, Carmen Oi Kwan2
  • Chan, Gordon Ho Ching1
  • Lau, Terrence Chi Kong2
  • Ngo, Jacky Chi Ki3
  • 1 School of Life Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China. , (China)
  • 2 Department of Biomedical Sciences, City University of Hong Kong, Kowloon, Hong Kong, China. , (China)
  • 3 School of Life Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China. Electronic address: [email protected] , (China)
Type
Published Article
Journal
Journal of Biological Chemistry
Publisher
American Society for Biochemistry and Molecular Biology
Publication Date
Jan 25, 2019
Volume
294
Issue
4
Pages
1312–1327
Identifiers
DOI: 10.1074/jbc.RA118.003392
PMID: 30478176
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Serine-arginine (SR) proteins are essential splicing factors containing a canonical RNA recognition motif (RRM), sometimes followed by a pseudo-RRM, and a C-terminal arginine/serine-rich (RS) domain that undergoes multisite phosphorylation. Phosphorylation regulates the localization and activity of SR proteins, and thus may provide insight into their differential biological roles. The phosphorylation mechanism of the prototypic SRSF1 by serine-arginine protein kinase 1 (SRPK1) has been well-studied, but little is known about the phosphorylation of other SR protein members. In the present study, interaction and kinetic assays unveiled how SRSF1 and the single RRM-containing SRSF3 are phosphorylated by SRPK2, another member of the SRPK family. We showed that a conserved SRPK-specific substrate-docking groove in SRPK2 impacts the binding and phosphorylation of both SR proteins, and the localization of SRSF3. We identified a nonconserved residue within the groove that affects the kinase processivity. We demonstrated that, in contrast to SRSF1, for which SRPK-mediated phosphorylation is confined to the N-terminal region of the RS domain, SRSF3 phosphorylation sites are spread throughout its entire RS domain in vitro Despite this, SRSF3 appears to be hypophosphorylated in cells at steady state. Our results suggest that the absence of a pseudo-RRM renders the single RRM-containing SRSF3 more susceptible to dephosphorylation by phosphatase. These findings suggest that the single RRM- and two RRM-containing SR proteins represent two subclasses of phosphoproteins in which phosphorylation statuses are maintained by unique mechanisms, and pose new directions to explore the distinct roles of SR proteins in vivo. © 2019 Long et al.

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