Tardigrades are famous for their ability to survive extreme conditions such as complete desiccation. Cytosolic abundant heat soluble proteins (CAHS), a type of tardigrade disordered protein, is essential for desiccation survival. Our Lab has found that purified CAHS D undergo gelation, which I hypothesize is stabilized by intramolecular interactions involving transient formation of secondary structure.
I investigated how pH impacts the secondary structure of CAHS D.
Low (10 g/L) and high (40 g/L) concentration samples of CAHS D were prepared in buffer at pH 5.5 and 8.0. Their secondary structures were measured and compared by using Attenuated Total Internal Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy. CAHS D’s N-terminal region contains histidine residues, whose pKa is between 5.5 and 8.0. At pH 8, 40 g/L CAHS D has 5±1 % more α-helix, 1±1% fewer turns and loops, 3.3±1.0% less random structures, and between 0.2±0.3% and 1.2±0.9% less β-sheet than at pH 5.5. Therefore, deprotonation of histidine increases the percentage of α-helix. Understanding the structure of CAHS D gels will aid in our understanding of its function
