Most mitochondrial preproteins carry a cleavable N-terminal presequence that mediates targeting to mitochondria and translocation across the mito-chondrial membranes. In this study, we characterized the presequence of the citrate carrier (CIC, tricarboxylate carrier) of rat liver mitochondria. The CIC presequence was found to be dispensable both for targeting to mitochondria and insertion into the inner membrane. Unlike the pre2 sequence of the related phosphate carrier, fusion of the CIC presequence to the cytosolic enzyme dihydrofolate reductase did not confer mito chondrial targeting, indicating that the CIC presequence does not act as a targeting signal. However, the presequence was required to keep the CIC in a soluble state. Mature CIC lacking the presequence was prone to aggregation. We conclude that mitochondrial presequences do not necessarily act as mediators of targeting. In the case of the CIC, the presequence appears to determine the folding state of the preprotein.
Biogenesis of rat mitochondrial citrate carrier (CIC): The N-terminal presequence facilitates the solubility of the preprotein but does not act as a targeting signal
ZARA, Vincenzo;FERRAMOSCA, Alessandra;
2003-01-01
Abstract
Most mitochondrial preproteins carry a cleavable N-terminal presequence that mediates targeting to mitochondria and translocation across the mito-chondrial membranes. In this study, we characterized the presequence of the citrate carrier (CIC, tricarboxylate carrier) of rat liver mitochondria. The CIC presequence was found to be dispensable both for targeting to mitochondria and insertion into the inner membrane. Unlike the pre2 sequence of the related phosphate carrier, fusion of the CIC presequence to the cytosolic enzyme dihydrofolate reductase did not confer mito chondrial targeting, indicating that the CIC presequence does not act as a targeting signal. However, the presequence was required to keep the CIC in a soluble state. Mature CIC lacking the presequence was prone to aggregation. We conclude that mitochondrial presequences do not necessarily act as mediators of targeting. In the case of the CIC, the presequence appears to determine the folding state of the preprotein.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
