Porin (protein)

Porins are pore-forming transmembrane proteins in the outer membrane of gram-negative bacteria, mitochondria and chloroplasts. They serve the mass transfer through the membrane.

They were discovered and named by Hiroshi Nikaido.

There is in all porins a matching design approach: they consist of a chain of 300-420 amino acids, leading to a 16 - or 18 -string is folded antiparallel β - barrel ( one strand corresponds to a β -sheet ). The wall of the pore is very thin; it only has the strength of an amino acid. Inside the porin is a bottleneck with some ionizable amino acids at which the transmission properties of the pore are determined.

If one examines the porins of different types, one finds that they are similar in many structural features. This indicates homology and can be used as evidence that it is in the porins to very conservative proteins that have changed little in the course of evolution.

Mitochondrial porin (Ø ~ 4 nm) in the outer mitochondrial membrane and allows for the free diffusion of molecules up to about 5000 Da. It is also called a VDAC (voltage dependend anion channel), as it allows the controlled passage of anionic molecules, such as chloride, phosphate or nucleotides.