Though it has been observed that proteins are mostly insulating electrically, these hair-like filaments termed as pili show metallic like conductivity. It has been found that the electronic arrangement and the tiny molecular distances provide the electrical conductivity to pili. The direct measurement of various physical properties present in Geobacter sulfurreducens pili reveals that they have metallic-like conductivity. However, certain studies even state that this conductivity is not based on the structures of G sulfurreducens pilus calculated from homology models.
Pili has been examined with rocking-curve X-ray diffraction and synchrotron X-ray microdiffraction. The result derived by both these methods shows a periodic 0.32 nanometre spacing in G sulfurreducens pili. The power of the 0.32-nanometre peak raises about 100-fold as the pH shifts from 10.5 to 2. This shows a structure-function connection for metallic-like conductivity that may be accredited to the overlapping orbitals of aromatic amino acids.
G sulfurreducens pilus’ homology model shows that the aromatic amino acids present in it are located at a distance of 0.3 to 0.4 nanometre. The research further states that the G sulfurreducens pili represents a class of electronically functional proteins that promote long distance electron transport with the help of the aromatic amino acids present in it.
This finding is of interest as this may lead to the use of these biological components in lightweight electronics thereby making them cost-effective and non-toxic. It may even act as a biological source of electricity for bioremediation.