Outer membrane protein G (OmpG) is a porin

Porin (protein)

Porins are beta barrel proteins that cross a cellular membrane and act as a pore through which molecules can diffuse. Unlike other membrane transport proteins, porins are large enough to allow passive diffusion, i.e., they act as channels that are specific to different types of molecules...

, a channel proteins in the outer membrane

Outer membrane

The bacterial outer membrane is found in Gram-negative bacteria. Its composition is distinct from that of the cytoplasmic membrane - among other things, the outer leaflet of the membrane includes a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and it is linked to the cell's...

 of Gram-negative bacteria.

Escherichia coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

OmpG forms a 14-stranded beta-barrel and in contrast to most porins, appears to function as a monomer. The central pore of OmpG is wider than other E. coli porins and it is speculated that it may form a non-specific channel for the transport of larger oligosaccharide

Oligosaccharide

An oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars...

s.