A role for a eukaryotic GrpE-related protein, Mge1p, in protein translocation.

Laloraya, Shikha; Gambill, B. Diane; Craig, Elizabeth A.

doi:10.1073/pnas.91.14.6481

Cited by 168 publications

(105 citation statements)

References 28 publications

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“…Assuming that GrpE functions as a monomer, mtHsp70 as a monomer and Hsp60 as a tetradecamer, mt-GrpE therefore appears about 10-times and 1 2-times less abundant than mt-Hsp70 and Hsp60, respectively. This is in accordance with the function of Ygelp as an ADP/ATP exchange catalyst during the cycles of protein binding and release by mt-Hsp70 which is an integral part of mitochondrial protein import and subsequent folding [6,23,26,27]. Consistent with this function of Ygelp we have further shown that a small fraction of rat mt-GrpE (but not Hsp60) resides in the membrane fraction of lysed mitochondria (data not shown).…”

Section: Mt-grpe and A Low Abundance Mitochondrial Protein Of Ubiquitousupporting

confidence: 86%

Isolation and characterisation of a cDNA encoding rat mitochondrial GrpE, a stress‐inducible nucleotide‐exchange factor of ubiquitous appearance in mammalian organs

1996

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In contrast to the E. coli chaperones DnaK, GroEL and GroES, cDNAs encoding mitochondrial homologues of DnaJ and GrpE from higher eukaryotes have yet to be reported. Based on peptide sequences, we have isolated a cDNA encoding a 217 residue nuclear encoded precursor of rat mitochondrial GrpE (mt-GrpE) including a typical mitochondrial presequence of 27 residues. Western blotting revealed that the 21 kDa GrpE homologue is present exclusively in the mitochondrial fraction where it comprises only ~ 0.03% of the total soluble protein, while Northern blotting showed that the mt-GrpE transcript is present in most if not all organs. By contrast to other mitochondrial chaperones, the levels of mt-GrpE and its transcript in cultured cells are only marginally increased in response to the proline analog L-azetidine 2-carboxylic acid but not by heat shock. Furthermore, members of the GrpE family exhibit a much lower degree of sequence identity than do the well studied members of the Hsp70, Hsp60 and Hspl0 families.

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Section: Mt-grpe and A Low Abundance Mitochondrial Protein Of Ubiquitousupporting

confidence: 86%

Isolation and characterisation of a cDNA encoding rat mitochondrial GrpE, a stress‐inducible nucleotide‐exchange factor of ubiquitous appearance in mammalian organs

1996

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“…More recently the cohort chaperones of mt-Hsp70, mitochondrial DnaJ, (Mdjlp) and mitochondrial GrpE (Mgelp) have been identified and characterized [12 15]. MtHsp70 and Mgelp have been recognized to constitute essential components of the mitochondrial protein import machinery [14][15][16][17]. In contrast, Mdjlp does not play an indispensible role in protein import.…”

Section: Introductionmentioning

confidence: 99%

Role of the mitochondrial DnaJ homologue, Mdj1p, in the prevention of heat‐induced protein aggregation

Prip‐Buus¹,

Westermann²,

Schmitt³

et al. 1996

FEBS Letters

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“…Similarly important are cochaperones that regulate the affinity for nucleotides of their Hsp70 partner. For example, most prokaryotic Hsp70s require a GrpE-type nucleotide exchange factor, which is termed Mge1 in mitochondria (11) and CGE1 in chloroplasts (12).…”

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confidence: 99%

Assistance for a Chaperone

Willmund

Hinnenberger

Nick

et al. 2008

Journal of Biological Chemistry

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Previous efforts aimed at the biochemical characterization of chloroplast HSP70B were hampered by the observation that recombinant HSP70B was inactive, i.e. incompetent of interacting with its nucleotide exchange factor CGE1. In addition, because heterologously expressed mitochondrial Hsp70 was inactive unless coexpressed with the escort protein Hep1, we wondered whether homologs of Hep1 existed in the chloroplast. Data base searches revealed that algae and higher plants indeed encode at least two HEP homologs, one predicted to be targeted to mitochondria, the others to chloroplasts. Using Chlamydomonas reinhardtii as plant model organism we demonstrate that this alga encodes an HEP homolog (termed HEP2) that is localized to the stroma. HEP2 is expressed constitutively as a low abundance protein with an apparent molecular mass of ϳ21 kDa. In cell extracts HEP2 interacts with HSP70B in an ATP-dependent fashion. Coexpression of HSP70B with HEP2 in Escherichia coli yielded high levels of CGE1-binding competent HSP70B, which also displayed ATPase activity. Inactive HSP70B was more prone to proteolysis than active HSP70B. Although inactive HSP70B interacted with HEP2, it could not be activated. Active HSP70B remained active for 48 h in the absence of HEP2, suggesting that HEP2 was not involved in maintaining HSP70B in an active state. However, some HSP70B expressed as a fusion protein with an N-terminal extension was activated when HEP2 was present during cleavage of the fusion protein, suggesting that in vivo HEP2 might be required for de novo folding of HSP70B after transit peptide cleavage.

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A role for a eukaryotic GrpE-related protein, Mge1p, in protein translocation.

Cited by 168 publications

References 28 publications

Isolation and characterisation of a cDNA encoding rat mitochondrial GrpE, a stress‐inducible nucleotide‐exchange factor of ubiquitous appearance in mammalian organs

Isolation and characterisation of a cDNA encoding rat mitochondrial GrpE, a stress‐inducible nucleotide‐exchange factor of ubiquitous appearance in mammalian organs

Role of the mitochondrial DnaJ homologue, Mdj1p, in the prevention of heat‐induced protein aggregation

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