  Segments with the amino acid sequence EKAYLRT appear in natural occurring
proteins both in $\alpha$-helices and $\beta$-sheets. For this reason, we have
use this peptide to study how secondary structure formation in proteins depends
on the local environment. Our data rely on multicanonical Monte Carlo
simulations where the interactions among all atoms are taken into account.
Results in gas phase are compared with that in an implicit solvent. We find
that both in gas phase and solvated EKAYLRT forms an $\alpha$-helix when not
interacting with other molecules. However, in the vicinity of a $\beta$-strand,
the peptide forms a $\beta$-strand. Because of this change in secondary
structure our peptide may provide a simple model for the $\alpha \to \beta$
transition that is supposedly related to the outbreak of Prion diseases and
similar illnesses.
