NMR STRUCTURES OF A MITOCHONDRIAL TRANSIT PEPTIDE FROM THE GREEN-ALGACHLAMYDOMONAS-REINHARDTII

The 26-amino-acid pre-sequence of the ATP synthase beta subunit that d irects the protein from the cytosol to mitochondria in the unicellular green alga Chlamydomonas reinhardtii has been synthesised and analyse d using NMR spectroscopy/circular dichroism and compared to a chloropl ast transit peptide from the same organism, The results demonstrate th at the peptide, though mainly unstructured in water, undergoes a stron g conformational change in a 36% water/64% 2,2,2-trifluoroethanol mixt ure, In this solvent condition, an alpha-helix was characterised by NM R from residue 2 to 26, Structure calculations under NMR restraints le ad to a population of models of which 60% are kinked at position 9-10, Structural analysis indicates two hydrophobic sectors on the models w ith a discontinuity at the 9-10 kink level, The structures suggest a d ifferent interaction mode with the mitochondrial membrane compared to the chloroplast transit peptide.