The distribution of α‐helix propensity along the polypeptide chain is not conserved in proteins from the same family

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Abstract
We address the question of whether the distribution of secondary structure propensities of the residues along the polypeptide chain (denominated here as secondary structure profiles) is conserved in proteins throughout evolution, for the particular case of α‐helices. We have analyzed by CD the conformation of peptides corresponding to the five α‐helices of two α/β parallel proteins (ComA and Ara). The large α‐helical population of peptide ComA‐4 detected by CD in aqueous solution has been confirmed by NMR. These proteins are members of the CheY and P21‐ras families, respectively, which have been studied previously in the same way (Muñoz V, Jiménez MA, Rico M, Serrano L, 1995, J Mol Biol 245:275–296). Comparison of the helical content of equivalent peptides reveals that protein α‐helix propensity profiles are not conserved. Some equivalent peptides show very different helical populations in solution and this is especially evident in very divergent proteins (ComA and CheY). However, all the peptides analyzed so far adopted an important population of helical conformations in the presence of 30% trifluoroethanol, indicating that there could be a conserved minimal requirement for helical propensity.

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