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J Biol Chem, Vol. 273, Issue 33, 21169-21177, August 14, 1998

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

Dean J. Naylor^§, Anna P. Stines, Nicholas J. Hoogenraad^§, and Peter B. Høj^**

From the  Department of Horticulture, Viticulture and Oenology, The University of Adelaide, Waite Campus, PMB1, Glen Osmond, South Australia, 5064, Australia, the ^** Australian Wine Research Institute, Glen Osmond, South Australia, 5064, Australia, and the ^§ School of Biochemistry, La Trobe University, Bundoora, Victoria, 3083, Australia

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 0.5 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 ~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.

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