Circular dichroism studies on the signal sequence of E. coli alkaline phosphatase indicate the presence of both α‐helix and β‐structure in hydrophobic environments

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Abstract
The conformations of a synthetic peptide corresponding to the signal sequence of E. coli alkaline phosphatase, Lys‐Gln‐Ser‐Thr‐Ile‐Ala‐Leu‐Ala‐Leu‐Leu‐Pro‐Leu‐Leu‐Phe‐Thr‐Pro‐Val‐Thr‐Lys‐Ala‐OCH3, have been examined in different environments by circular dichroism spectroscopy. In trifluoroethanol, methanol and aqueous mixtures of these solvents, the signal peptide has largely random conformation (~80%) with small amounts of a‐helix and β‐structure. However, in micellar environment, there is a significant increase in ordered conformation with both α‐helix and β‐structure being present, unlike in other signal sequences reported in the literature, where only the α‐helical conformation has been observed. Hence, an α‐helical conformation may not be as stringent a requirement as overall hydrophobicity for recognition of signal sequences by the cell's export machinery.