1H NMR studies of prototypical helical designer peptides A comparative study of the amide chemical shift dependency on temperature and polypeptide sequence

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Abstract
A series of designer α-helical peptides with hydrophobic residues located at different positions along the sequence (PH-1.0 =LYQELQKLTQTLK, PH-1.19 =LYQELQKLTQTLFK, PH-1.12 =LYQELQKL LQTLK,PH-1.13 =LYQELQKLTLTLK,PH-1.4 =LYQELQKLTQTTK) were analyzed using one- and two-dimensional NMR methods (TOCSY and NOESY). The central feature of these designer peptides is the incorporation of a maximal hydrophobic strip which may play a role in antigen processing and the nucleation of α-helices in proteins (J. Immunol.145, 899, 1990). Using the 2D-NMR, sequence specific assignments and NOE connectivities were determined in all peptides when dissolved in H2O/TFE mixtuRes NOE connectivities indicated that all these peptides are helical in this medium. An unusually large number of NOEs was found for all these designer peptides. This is in accord with ultracentrifugation studies that showed that PH-1.0 forms a trimer in 50% H2O/TFE mixtures. Other peptides in the series behave in similar manner as PH-1.0. The structural differences among these peptides was addressed using the backbone amide chemical shift temperature coefficients, ∇, and the differences between the observed and random coil values, ΔδHN. The ΔδHN patterns along the peptide sequence are consistent with those expected for amphiphilic α-helices, where most ΔδHN values are below zero. However, no significant differences among the peptides in this series can be detected on the ΔδHN patterns, with the exception of PH-1.12. The ∇ values reveal differences among the peptides of the series. The patterns of ∇ along the peptide sequences are similar to that found for ΔδHN for PH-1.0, PH-1.19 and PH-1.4. The other peptides in the series, PH-1.12 and PH-1.13, showed different patterns for ∇. The latter parameter was used to evaluate the helicity of this series of peptides. According to this parameter the relative helicity of this series is as follows: PH-1.12 < PH-I .O < PH-1.4 < PH-1.19 < PH-1.13 The NMR data shown here correlated well with the helical propensities predicted for polypeptide sequences using statistical arguments (Proc. Nutl. Acad Sci. USA, 90, 9100, 1993). 0 Munksgaard 1996.