Conformational study of the Thr-Gly repeat in theDrosophilaclock protein, PERIOD

Recent results with the Drosophila melanogaster period gene suggest that the apparently conserved repetitive motif (Thr-Gly)$_{n}$ encoded by this gene may play an important role in the temperature compensation of the circadian clock. We have therefore initiated both a theoretical and experimental conformational analysis of (Thr-Gly)$_{n}$ peptides. By using a build-up method, it is clear that the hexapeptide (Thr-Gly)$_{3}$ represents a `conformational monomer' and generates a stable type II or type III $\beta $-turn. Circular dichroism and nuclear magnetic resonance spectra of synthetic (Thr-Gly)$_{3}$ and poly (Thr-Gly) peptides revealed that these peptides exhibit flexible conformations, especially in more polar environments and at higher temperatures. We speculate that this flexibility may illuminate our understanding of both the molecular mechanism of temperature compensation and the systematic geographical distribution within Europe of the Thr-Gly length polymorphism in D. melanogaster.