Structure of the signal sequences for two mitochondrial matrix proteins that are not proteolytically processed upon import.
The N-terminal sequences of rhodanese and 3-oxoacyl-CoA thiolase, two mitochondrial matrix proteins that are not proteolytically processed upon import, have been studied by NMR and CD spectroscopy. In aqueous trifluoroethanol, in the presence of micelles, and in the presence of small unilamellar vesicles (SUVs), these peptides form alpha-helical structures beginning near the N-terminus and extending, continuously, for at least three helical turns. This result is consistent with a previous finding that a mutant rat liver mitochondrial aldehyde dehydrogenase signal sequence we designed, which formed a continuous alpha-helix, could successfully direct protein import but was not proteolytically processed (Thornton, K., Wang, Y., Weiner, H., & Gorenstein, D. G. (1993) J. Biol. Chem. 268, 19906-19914). From these three examples, a model is developed which suggests that a mitochondrial signal sequence that has an N-terminal alpha-helix longer than 11 residues can take on the necessary conformation to be imported but cannot adopt the necessary conformation to be processed.
Hammen
P K
PK
Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907.
Gorenstein
D G
DG
Weiner
H
H
D000101:Acetyl-CoA C-Acetyltransferase / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002942:Circular Dichroism; D008081:Liposomes / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D008928:Mitochondria / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D051381:Rats; D012996:Solutions; D013884:Thiosulfate Sulfurtransferase / Q000737:chemistry* / Q000378:metabolism; D014270:Trifluoroethanol
D008081:Liposomes; D008823:Micelles; D021382:Protein Sorting Signals; D012996:Solutions; D014270:Trifluoroethanol; D000101:Acetyl-CoA C-Acetyltransferase; D013884:Thiosulfate Sulfurtransferase