Abstract
We here report systematic study of structural dynamics of a 16-residue self-assembling peptide d-EAK16 made of only D-amino acids. We compare these results with its chiral counterpart L-form, l-EAK16. Circular dichroism was used to follow the structural dynamics under various temperature and pH conditions. At 25°C the d-EAK16 peptide displayed a typical beta-sheet spectrum. Upon increasing the temperature above 70°C, there was a spectrum shift as the 218 nm valley widens toward 210 nm. Above 80°C, the d-EAK16 peptide transformed into a typical alpha-helix CD spectrum without going through a detectable random-coil intermediate. When increasing the temperature from 4°C to 110°C then cooling back from 110°C to 4°C, there was a hysteresis: the secondary structure from beta-sheet to alpha-helix and then from alpha-helix to beta-sheet occurred. d-EAK16 formed an alpha-helical conformation at pH0.76 and pH12 but formed a beta-sheet at neutral pH. The effects of various pH conditions, ionic strength and denaturing agents were also noted. Since D-form peptides are resistant to natural enzyme degradation, such drastic structural changes may be exploited for fabricating molecular sensors to detect minute environmental changes. This provides insight into the behaviors of self-assembling peptides made of D-amino acids and points the way to designing new peptide materials for biomedical engineering and nanobiotechnology.
Highlights
Chirality plays an absolutely central role in all life forms
We report on its structural dynamics in terms of thermal stability, pH changes, ionic strength and chemically denaturing agents
Molecular models of d-EAK16 and l-EAK16 We present two molecular models of the chiral EAK16 peptides (Fig. 1)
Summary
Chirality plays an absolutely central role in all life forms. There are chemically possible D- and L- amino acids, natural proteins are made of only L-amino acids. Why the chirality of life is asymmetric and why nature only uses Lamino acid and D-sugars are tantalizing questions. In the past decades there has been much effort focused on the study of various self-assembling peptides and their relevance in biology, protein aggregation, and their applications in biotechnology and nanobiotechnology [1,2,3,4,5]. Not surprisingly most of this work has been carried out using the naturally occurring L-form amino acid [1,2,3,4,5]
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