GRIM-19 Is Essential for Maintenance of Mitochondrial Membrane Potential

Hao Lu and Xinmin Cao

Signal Transduction Laboratory, Institute of Molecular and Cell Biology, Singapore 138673, The Republic of Singapore

Monitoring Editor: Donald Newmeyer

GRIM-19 was found to copurifywith complex I of mitochondrial respiratory chain, and subsequentlydemonstrated to be involved in complex I assembly and activity.To further understand its function in complex I, we dissectedits functional domains by generating a number of deletion, truncation,and point mutants. The mitochondrial localization sequenceswere located at the N-terminus. Strikingly, deletion of residues70–80, 90–100, or the whole C-terminal region (70–144),led to a loss of mitochondrial transmembrane potential ( ${Delta}$ ${Psi}$ m).However, similar deletions of another two complex I subunits,NDUFA9 and NDUFS3, did not show such effect. We also found thatdeletion of the last 10 residues affected GRIM-19’s abilityto be assembled to complex I. We constructed a dominant-negativemutant containing the N-terminal 60 and the last C-terminal10 residues which could be assembled into complex I, but failedto maintain normal ${Delta}$ ${Psi}$ m. Cells overexpressing this mutant did notspontaneously undergo cell death, but were sensitized to apoptosisinduced by cell death agents. Our results demonstrate that GRIM-19is required for electron transfer activity of complex I, anddisruption of ${Delta}$ ${Psi}$ m by GRIM-19 mutants enhances the cells’sensitivity to apoptotic stimuli.

Address correspondence to: Xinmin Cao (mcbcaoxm{at}imcb.a-star.edu.sg)