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

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-OCH 3, 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.