Projects

Turn residues as well as side-chain interactions play an important role for the folding of ß-sheets. We investigated the conformational dynamics of a three-stranded ß-sheet peptide (^DP^DP) and a two-stranded ß-hairpin (WVYY-^DP) by time-resolved temperature-jump infrared spectroscopy. Both peptide sequences contain ^DPro-Gly residues that favor a tight ß-turn. The three-stranded ß-sheet (Ac-VFITS^DPGKTYTEV^DPGOKILQ-NH₂) is stabilized by the turn sequences, whereas the ß-hairpin (SWTVE^DPGKYTYK-NH₂) folding is assisted both by the turn sequence and by hydrophobic cross-strand interactions. Relaxation times after the T-jump were monitored as a function of temperature and occur on a sub-microsecond time scale, ^DP^DP being faster than WVYY-^DP. The Xxx-^DPro tertiary amide provides a detectable IR band allowing us to site-specifically probe the dynamics. The relative importance of the turn versus the intra-strand stability in ß-sheet formation is discussed.

TtoA is a major outer membrane protein (Omp) with β-barrel structure from the thermophilic eubacterium T. thermophilus. FT-IR spectroscopy and SDS PAGE analysis were used to monitor the stability of detergent-solubilised TtoA under denaturing conditions. Heat as well as the common denaturants urea and SDS were applied to affect the TtoA structure. The protein has proven to be extremely thermostable in its native form. Denaturants likewise only have little effects on the protein's structure. In detail, a SDS concentration of 1% as is typical for Laemmli buffer does not have an impact on the structure of TtoA, even in combination with a temperature of 99°C. The same holds true for urea concentrations below 8 M. Only the combination of highly concentrated urea or SDS in combination with incubating the protein at 99°C for 10 minutes leads to a change of the secondary structure in TtoA.