However, it has recently been reported that other genes, including DnaJ heat shock protein family (Hsp40) member C21 (DNAJC21), elongation factor-like 1 (EFL1) and signal recognition particle 54 (SRP54) are also associated with an SDS-like phenotype.
The mutual effects of Sdo1 and nucleotides on Efl1 modulate in a very specific and robust way the complex conformational landscape of Efl1, resembling the behavior observed with other GTPases and their cofactors.
Building on the recent observation that EFL1 single-point mutations clinically manifest as SDS-like phenotype, we carried out comparative Molecular Dynamics (MD) simulations on three mutants, T127A, M882K and R1095Q and wild type EFL1.
Additionally, we studied the interaction mechanism of the proteins in solution and demonstrated that binding consists of two independent and cooperative events, with domains 2⁻3 of SBDS directing the initial interaction with EFL1, followed by docking of domain 1.
Similar to the molecular pathology of SDS, mutant EFL1 proteins do not promote the release of cytoplasmic Tif6 from the 60S subunit, likely preventing the formation of mature ribosomes.
Association of EFL1 to SBDS did not modify the affinity for GTP but dramatically decreased that for GDP by increasing the dissociation rate of the nucleotide.
We characterized the structural content and folding stability of the Saccharomyces cerevisiae and human EFL1 GTPases, as well as their enzymatic properties alone and in the presence of Sdo1 and SBDS, respectively.
Our findings establish a direct role for SBDS and EFL1 in catalyzing the translational activation of ribosomes in all eukaryotes, and define SDS as a ribosomopathy caused by uncoupling GTP hydrolysis from eIF6 release.