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ERAD of KHN, how ever, was strongly defective in the sec61L7 mutant in contrast to ERAD of its membrane anchored counterpart KWW whose half life improved only moderately. Considering that KHN Epothilone B tumor and KWW are already shown by Vashist and Ng to get identical chaperone specifications for ERAD, this experiment demonstrates that rather than affecting indirectly the chaperone composition from the ER lumen sec61L7 features a direct damaging result on export in the ER of soluble substrates only. The sec61Y345H mutant had no growth defect at any temperature, and also a tunicamycin sensitivity comparable to sec61 32 and sec61 three. It was entirely functional in protein import into the ER suggesting that this place in L7 could play a part during the initiation of Sec61 channel opening from your lumenal side for ex port of ERAD substrates.
One particular would anticipate a mild phenotype so as for mice to survive this mutation in an important gene. Delayed ER export in pancreatic beta cells which possess a higher secretory protein load would lead to gradual ER accumulation of misfolded proteins, followed by cell death, as well as the growth of diabetes like a principal phenotype. The delay during the initiation of ERAD inFlavopiridol (Alvocidib) sec61Y345H yeast is reminiscent with the delay in protein import observed by Trueman et al. in L7 mutants that disrupt the interaction of L7 with TMD7. Taken together, our data recommend that L7 conformation is important for Sec61 channel gating for the two import and ERAD of soluble proteins.
Modelling of the Sec61L7 protein suggests that the plug formed by transmembrane helix 2a remains in area, however the lateral gate formed by interaction of trans membrane helix 2b with transmembrane helix seven is par tially open, as helix 2b is shifted drastically towards the cytoplasmic surface from the membrane. This shift is likely the consequence on the missing lumenal finish of TMD7 which might no longer interact with helix 2b and hold it in spot. The deletion in Sec61L7p starts 2 amino acids C terminal of N302 which can be one of the most C terminal residue of your gating motif responsible for setting the hydrophobicity threshold for entry of signal sequences in to the Sec61 channel. Destabilizing the gating motif by changing N302 with far more polar amino acids triggers promiscuous insertion of even marginally hydrophobic signal peptides in to the gate. In SecL7pdespite N302 is underneath strain since it is now close to the end of trun cated TMD7 that's connected to TMD8 by only two amino acids. This can weaken the hydrogen bonds to N302 partners while in the gating motif which probable explains the partial opening of your gate. Even though the destabilization on the lateral gate inside the Sec61L7 channel is much like that of your N302 to polar mutants, in contrast to Trueman et al.