Cancer-relevant splicing factor CAPERalpha engages the essential splicing factor SF3b155 in a specific ternary complex.
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Loerch S, Maucuer A, Manceau V, Green MR, Kielkopf CL
Cancer-relevant splicing factor CAPERalpha engages the essential splicing factor SF3b155 in a specific ternary complex.
J Biol Chem. 2014 Jun 20;289(25):17325-37. doi: 10.1074/jbc.M114.558825. Epub 2014 May 2.
- PubMed ID
- 24795046 [ View in PubMed]
- Abstract
U2AF homology motifs (UHMs) mediate protein-protein interactions with U2AF ligand motifs (ULMs) of pre-mRNA splicing factors. The UHM-containing alternative splicing factor CAPERalpha regulates splicing of tumor-promoting VEGF isoforms, yet the molecular target of the CAPERalpha UHM is unknown. Here we present structures of the CAPERalpha UHM bound to a representative SF3b155 ULM at 1.7 A resolution and, for comparison, in the absence of ligand at 2.2 A resolution. The prototypical UHM/ULM interactions authenticate CAPERalpha as a bona fide member of the UHM family of proteins. We identify SF3b155 as the relevant ULM-containing partner of full-length CAPERalpha in human cell extracts. Isothermal titration calorimetry comparisons of the purified CAPERalpha UHM binding known ULM-containing proteins demonstrate that high affinity interactions depend on the presence of an intact, intrinsically unstructured SF3b155 domain containing seven ULM-like motifs. The interplay among bound CAPERalpha molecules gives rise to the appearance of two high affinity sites in the SF3b155 ULM-containing domain. In conjunction with the previously identified, UHM/ULM-mediated complexes of U2AF(65) and SPF45 with SF3b155, this work demonstrates the capacity of SF3b155 to offer a platform for coordinated recruitment of UHM-containing splicing factors.