Evidence for the Existence of Distinct Mammalian Cytosolic, Microsomal, and Two Mitochondrial GrpE-like Proteins, the Co-chaperones of Specific Hsp70 Members

• Published in: The Journal of biological chemistry 1998-08, Vol.273 (33), p.21169-21177
• Main Authors: Naylor, Dean J., Stines, Anna P., Hoogenraad, Nicholas J., Høj, Peter B.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Cytosol - metabolism; DNA, Complementary; Heat-Shock Proteins - genetics; Heat-Shock Proteins - metabolism; HSP70 Heat-Shock Proteins - genetics; HSP70 Heat-Shock Proteins - metabolism; Mice; Microsomes - metabolism; Mitochondria - metabolism; Molecular Chaperones - genetics; Molecular Chaperones - metabolism; Molecular Sequence Data; Rats; Sequence Homology, Amino Acid; Tumor Cells, Cultured
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.33.21169

We previously reported the cDNA cloning and characterization of a mammalian mitochondrial GrpE protein (∼21 kDa, mt-GrpE#1) and now provide evidence for the presence of distinct cytosolic (∼40 kDa), microsomal (∼50 kDa), and additional mitochondrial (∼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 0.5m 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 ∼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.