Regulation of mitochondrial protein import by the nucleotide exchange factors GrpEL1 and GrpEL2 in human cells

Abstract

Mitochondria are organelles indispensable for maintenance of cellular energy homeostasis. Most mitochondrial proteins are nuclearly encoded and are imported into the matrix compartment where they are properly folded. This process is facilitated by the mitochondrial heat shock protein 70 (mtHsp70), a chaperone contributing to mitochondrial protein quality control. The affinity of mtHsp70 for its protein clients and its chaperone function are regulated by binding of ATP/ADP to mtHsp70's nucleotide-binding domain. Nucleotide exchange factors (NEFs) play a crucial role in exchanging ADP for ATP at mtHsp70's nucleotide-binding domain, thereby modulating mtHsp70's chaperone activity. A single NEF, Mge1, regulates mtHsp70's chaperone activity in lower eukaryotes, but the mammalian orthologs are unknown. Here, we report that two putative NEF orthologs, GrpE-like 1 (GrpEL1) and GrpEL2, modulate mtHsp70's function in human cells. We found that both GrpEL1 and GrpEL2 associate with mtHsp70 as a hetero-oligomeric subcomplex and regulate mtHsp70 function. The formation of this subcomplex was critical for conferring stability to the NEFs, helped fine-tune mitochondrial protein quality control, and regulated crucial mtHsp70 functions, such as import of preproteins and biogenesis of Fe-S clusters. Our results also suggested that GrpEL2 has evolved as a possible stress resistance protein in higher vertebrates to maintain chaperone activity under stress conditions. In conclusion, our findings support the idea that GrpEL1 has a role as a stress modulator in mammalian cells and highlight that multiple NEFs are involved in controlling protein quality in mammalian mitochondria.

The LIV-1-GRPEL1 axis adjusts cell fate during anti-mitotic agent-damaged mitosis

“…Currently, the function of human GRPEL1 is not known. GR-PEL1 is a mitochondria-localized protein in E. coli and has been proposed to act as a co-chaperone [33][34][35] . In this study, however, GRPEL1 protein displayed a diffuse intracellular distribution, which display in cytoplasm and nucleus localization and didn't display any mitochondrial locazation (Fig.…”

Post Genomics Identification of Blood Stage Invasins of Plasmodium Falciparum

“…Interestingly, the reactive oxygen species (ROS) sensing function of NEF remained conserved during evolution. GrpEL1, the human ortholog of Mge1, acts as a ROS sensor and is associated with reduced expression and better cell survivability under high ROS conditions (Srivastava et al, 2017). However, Mge1 has diverged into a second paralog GrpEL2, specifically in chordates, which is resistant to oxidative stress and probably responsible for maintaining baseline mitochondrial activity under stress conditions (Naylor et al, 1998;Srivastava et al, 2017).…”

“…GrpEL1, the human ortholog of Mge1, acts as a ROS sensor and is associated with reduced expression and better cell survivability under high ROS conditions (Srivastava et al, 2017). However, Mge1 has diverged into a second paralog GrpEL2, specifically in chordates, which is resistant to oxidative stress and probably responsible for maintaining baseline mitochondrial activity under stress conditions (Naylor et al, 1998;Srivastava et al, 2017). In contrast to NEF homodimer of lower eukaryotes, human NEFs GrpEL1 and GrpEL2 function as heterodimer under normal conditions (Srivastava et al, 2017) (Fi.…”

Estudos da interação entre a mortalina humana e as duas isoformas das co-chaperonas GrpEs

“…Normalmente, como foi demonstrado naquele estudo, isso é evitado pela ação da proteína hHep1, sendo ela inclusive utilizada como estratégia de co-expressão para que a mortalina possa ser produzida solúvel (DORES-SILVA et al, 2015b (ALLU et al, 2018;KONOVALOVA et al, 2018;SRIVASTAVA et al, 2017) , é plausível supor que elas atuem em situações de estresse oxidativo, já que o interior da mitocôndria é o sítio principal desse tipo de estresse. Seguindo essa linha de pensamento, estudos preliminares das GrpEs em diferentes estados oxidativos foram iniciados.…”

“…Há indicações de que elas possuem padrão de expressão diferentes(NAYLOR et al, 1998) e que poderiam, por mecanismos como a regulação pós-transcricional, atuarem em diferentes condições celulares.Tradicionalmente, as GrpEs bacterianas têm sido associadas a uma função de termosensora molecular, mas no caso das GrpEs mitocondriais humanas não há evidências de que elas possuem essa mesma função. Trabalhos recentes(ALLU et al, 2018;KONOVALOVA et al, 2018;SRIVASTAVA et al, 2017) indicaram um possível papel no contexto do estresse oxidativo. Mais detalhes serão abordados adiante.…”