Left-handed Structure
In principle, a left-handed version of the π-helix is possible by reversing the sign of the (φ, ψ) dihedral angles to (55°, 70°). This pseudo-"mirror-image" helix has roughly the same number of residues per turn (4.1) and helical pitch (1.5 angstroms or 150 picometers). It is not a true mirror image, because the amino-acid residues still have a left-handed chirality. A long left-handed π-helix is unlikely to be observed in proteins because, among the naturally occurring amino acids, only glycine is likely to adopt positive φ dihedral angles such as 55°.
Read more about this topic: Pi Helix
Famous quotes containing the words left-handed and/or structure:
“Two left-handed gloves don’t make a pair. Two half-truths don’t make a truth.”
—Multatuli [Eduard Douwer Dekker] (1820–1887)
“Vashtar: So it’s finished. A structure to house one man and the greatest treasure of all time.
Senta: And a structure that will last for all time.
Vashtar: Only history will tell that.
Senta: Sire, will he not be remembered?
Vashtar: Yes, he’ll be remembered. The pyramid’ll keep his memory alive. In that he built better than he knew.”
—William Faulkner (1897–1962)