2POR is a bacterial porin from Rhodobacter Capsulatus.

Function:
Porins are transmembrane proteins used to transport sugars and nutrients across cell membranes. They allow non-specific polar molecules of less than approximately 600 daltons cross the membrane. In general, porins are more resistent to denaturing by heat or detergents than most proteins.
The porin described here is a bacterial porin used on the outer membrane of a bacteria. Another common porin is found on the mitocondrial membrane. This porin is reponsible for the voltage differential across the mitocondrial membrane that allows mitocondria to generate ATP.

Structure:
Porins are predominantly beta strands, unlike many transmembrane proteins that are mainly alpha helixes. The Rhodobacter porin consists of 16 beta strands rolled into a barrel, as seen in the picture. The quaternary structure of the protein is a three barrels side-by-side.

Experiment Parameters:
The 2POR structure was determined in 1992 by M. S. Weiss and G. E. Schulz.

• The structure was solved using X-ray crystallography
• The resolution was 1.8 angstroms, with a resolution range of 10 to 1.8 angstroms
• R Factor = 0.186
• Final model included the 301 peptide chains, 3 calcium ions, 274 solvent molecules modeled as water, and 4 molecules modeled as the detergent N-Octyltetraoxyethylene
• The unit cell had the dimension (in angstroms) of a=92.30, b=92.30, c=146.20 with angles alpha=90, beta=90, and gamma=120
• Space Group = R 3