The biological unit of 5eon () is a crystallographic structure of 6 alpha helices assembled into a fiber with a hydrophobic core[1]. The individual peptides are synthetic and were designed to assemble in this manner, with a hydrophotic core rich in phenylalanine. The crystal structure has a resolution of 1.7 Å (very good), and an Rfree of 0.22, which is average for this resolution, indicating that the model is reliable.
The . The Phe rings (dark gray) are surrounded by (light gray).
The is mostly charged Lys+ and Glu- sidechains, with an occasional Trp or Gln, interspersed with Ala (spheres).
The charges form on the surface, reminiscent of Xiao's theoretical model of the Geobacter sulfurreducens pilus. Unlike Xiao's model, none of these form salt bridges (a few opposite charges are water-bridged). Cation-pi interactions involving Phe cannot form since Phe is buried and Lys is on the surface. A few cation-pi interactions may form between Trp on the surface and Lys.
Sequence
The peptide sequence is constructed from 4 copies of heptad
E L/F K A I A Q/K/W
The amino-terminal Glu is acetylated, removing its positive charge. The C-terminal Lys is amidated, removing its negative charge. Here is the sequence of one complete peptide (29 amino acids) showing the heptad repeats.
ELKAIAQ EFKAIAK EFKAIAW EFKAIAQ K
