The inactive C-terminal cassette of the dual-cassette RNA helicase BRR2 both stimulates and inhibits the activity of the N-terminal helicase unit.Vester, K., Santos, K.F., Kuropka, B., Weise, C., Wahl, M.C.
(2020) J Biol Chem 295: 2097-2112
- PubMed: 31914407
- DOI: https://doi.org/10.1074/jbc.RA119.010964
- Primary Citation of Related Structures:
6S8O, 6S8Q, 6S9I
- PubMed Abstract:
The RNA helicase bad response to refrigeration 2 homolog (BRR2) is required for the activation of the spliceosome before the first catalytic step of RNA splicing. BRR2 represents a distinct subgroup of Ski2-like nucleic acid helicases whose members comprise tandem helicase cassettes. Only the N-terminal cassette of BRR2 is an active ATPase and can unwind substrate RNAs. The C-terminal cassette represents a pseudoenzyme that can stimulate RNA-related activities of the N-terminal cassette. However, the molecular mechanisms by which the C-terminal cassette modulates the activities of the N-terminal unit remain elusive. Here, we show that N- and C-terminal cassettes adopt vastly different relative orientations in a crystal structure of BRR2 in complex with an activating domain of the spliceosomal Prp8 protein at 2.4 Å resolution compared with the crystal structure of BRR2 alone. Likewise, inspection of BRR2 structures within spliceosomal complexes revealed that the cassettes occupy different relative positions and engage in different intercassette contacts during different splicing stages. Engineered disulfide bridges that locked the cassettes in two different relative orientations had opposite effects on the RNA-unwinding activity of the N-terminal cassette, with one configuration enhancing and the other configuration inhibiting RNA unwinding compared with the unconstrained protein. Moreover, we found that differences in relative positioning of the cassettes strongly influence RNA-stimulated ATP hydrolysis by the N-terminal cassette. Our results indicate that the inactive C-terminal cassette of BRR2 can both positively and negatively affect the activity of the N-terminal helicase unit from a distance.
Structural Biochemistry Group, Department of Biochemistry, Freie Universität Berlin, Takustrasse 63, D-14195 Berlin, Germany; Macromolecular Crystallography Group, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany. Electronic address: email@example.com.