Evidence for the existence of distinct mammalian cytosolic, microsomal, and two mitochondrial GrpE-like proteins, the Co-chaperones of specific Hsp70 members.
We previously reported the cDNA cloning and characterization of a mammalian mitochondrial GrpE protein ( approximately 21 kDa, mt-GrpE#1) and now provide evidence for the presence of distinct cytosolic ( approximately 40 kDa), microsomal ( approximately 50 kDa), and additional mitochondrial ( approximately 22 kDa, mt-GrpE#2) GrpE-like members. While a cytosolic GrpE-like protein has recently been identified, the demonstration of both a microsomal and a second mitochondrial GrpE-like member represents the first in any biological system. Investigation of the microsomal and two mitochondrial GrpE-like proteins revealed that they bound specifically to Escherichia coli DnaK, and the complexes formed were not disrupted in the presence of 0.5 M salt but were readily dissociated in the presence of 5 mM ATP. The functional integrity of mt-GrpE#1 and #2 was verified by their ability to specifically interact with and stimulate the ATPase activity of mammalian mitochondrial Hsp70 (mt-Hsp70). Analysis of the cDNA sequences encoding the two mammalian mitochondrial GrpE-like proteins revealed approximately 47% positional identity at the amino acid level, the presence of a highly conserved mitochondrial leader sequence, and putative destabilization elements within the 3'-untranslated region of the mt-GrpE#2 transcript which are not present in the mt-GrpE#1 transcript. A constitutive expression of both mitochondrial GrpE-like transcripts in 22 distinct mouse tissues was observed but possible different post-transcriptional regulation of the mt-GrpE#1 and #2 transcripts may confer a different expression pattern of the encoded proteins.
Department of Horticulture, Viticulture and Oenology, The University of Adelaide, Waite Campus, PMB1, Glen Osmond, South Australia, 5064, Australia. dnaylor@waite.adelaide.edu.au
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Naylor
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Hoogenraad
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003600:Cytosol / Q000378:metabolism*; D018076:DNA, Complementary; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008861:Microsomes / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D051381:Rats; D017386:Sequence Homology, Amino Acid; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; C109172:GrpE-like 1 mitochondrial protein, vertebrate; C484656:Grpel1 protein, mouse; C484655:Grpel1 protein, rat; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones