The helix nucleation site and propensity of the synthetic mitochondrial presequence of ornithine carbamoyltransferase
2000
de Jongh, Harmen H. J.
This study describes the helix nucleation site and helix propagation of the amphiphilic helical structure of the mitochondrial presequence of rat ornithine carbamoyltransferase. We investigated this property of the 32âresidue synthetic presequence using CD and 2DâHR NMR techniques by determining the structure as a function of the concentration of trifluoroethanol. It was found that the hydrophobic cluster Ile7âLeu8âLeu9 forms the helix nucleation site, expanding to include residues Asn4 to Lys16 when the concentration of trifluoroethanol is increased from 10 to 30%. At higher trifluoroethanol concentrations an increased ‘stiffening’ of the polypeptide backbone (to Arg26) is observed. In addition, by recording CD spectra at different trifluoroethanol concentrations as a function of temperature, it was found that the equilibrium constant between helix and random coil formation for this peptide exhibits a strong temperature dependence with maximum values between 20 and 30â°C. Comparison of these equilibrium constants with those of homopolymers stressed the unique character of the mitochondrial presequence. The findings are discussed in relation to the molecular recognition events at different stages of the transport process of this protein into mitochondria.
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