The requirement of heat shock cognate 70 protein for mitochondrial import varies among precursor proteins and depends on precursor length.

AUTOR(ES)

Terada, K

RESUMO

The cytosolic heat shock cognate 70-kDa protein (hsc70) is required for efficient import of ornithine transcarbamylase precursor (pOTC) into rat liver mitochondria (K. Terada, K. Ohtsuka, N. Imamoto, Y. Yoneda, and M. Mori, Mol. Cell. Biol. 15:3708-3713, 1995). The requirement of hsc70 for mitochondrial import of various precursor proteins and truncated pOTCs was studied by using an in vitro translation import system in which hsc70 was completely depleted. hsc70-dependent import of pOTC was about 60% of the total import, while import of the aspartate aminotransferase precursor, the serine:pyruvate aminotransferase precursor, and 3-oxoacyl coenzyme A thiolase was about 50, 30, and 0%, respectively. The subunit sizes of these four precursor proteins were 40 to 47 kDa. When pOTC was serially truncated from the COOH terminal, the hsc70 requirement decreased gradually and was not evident for the shortest truncated pOTCs of 90 and 72 residues. These truncated pOTCs were imported and proteolytically processed rapidly in 0.5 to 2 min at 25 degrees C, and the processed mature portions and the presequence portion were rapidly degraded. Sucrose gradient centrifugation analysis followed by import assay showed that pOTC synthesized in rabbit reticulocyte lysate forms an import-competent complex of about 11S in an hsc70-dependent manner. S values of import-competent forms of aspartate aminotransferase precursor, serine:pyruvate aminotransferase precursor, and 3-oxoacyl coenzyme A thiolase were 9S, 9S, and 4S, respectively. Thus, the S value decreased as the hsc70 dependency decreased. Precursor proteins were coimmunoprecipitated from the reticulocyte lysate containing the newly synthesized precursor proteins with an hsc70 antibody. The amount of coimmunoprecipitated proteins was much larger in the absence of ATP than in its presence. Among the four precursor proteins, the amount of coimmunoprecipitated protein decreased as the hsc70 dependency decreased.

Documentos Relacionados

• Role of heat shock cognate 70 protein in import of ornithine transcarbamylase precursor into mammalian mitochondria.
• Molecular identification and expression of heat shock cognate 70 (hsc70) and heat shock protein 70 (hsp70) genes in the Pacific oyster Crassostrea gigas
• The transport of proteins into the nucleus requires the 70-kilodalton heat shock protein or its cytosolic cognate.
• Expression of 65- and 67-kilodalton heat-regulated proteins and a 70-kilodalton heat shock cognate protein of Leishmania donovani in macrophages.
• Heat Shock Cognate Protein 70 Is Involved in Rotavirus Cell Entry