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.
Most mitochondrial preproteins carry a cleavable N-terminal presequence that mediates targeting to mitochondria and translocation across the mitochondrial 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 presequence of the related phosphate carrier, fusion of the CIC presequence to the cytosolic enzyme dihydrofolate reductase did not confer mitochondrial 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.
Zara
Vincenzo
V
Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università di Lecce, Via Provinciale Lecce-Monteroni, Italy. vincenzo.zara@unile.it
Ferramosca
Alessandra
A
Palmisano
Ilaria
I
Palmieri
Ferdinando
F
Rassow
Joachim
J
D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D019286:Endopeptidase K / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism*; D017510:Protein Folding; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism*; D021382:Protein Sorting Signals; D021381:Protein Transport / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
D002352:Carrier Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; C020723:citrate-binding transport protein; D013762:Tetrahydrofolate Dehydrogenase; D014357:Trypsin; D019286:Endopeptidase K