β-Barrel porins. These proteins form transmembrane pores that usually allow the energy independent passage of solutes across a membrane. The transmembrane portions of these proteins consist exclusively of β-strands which form a β-barrel. These porin-type proteins are found in the outer membranes of Gram-negative bacteria, mitochondria, plastids and possibly acid-fast Gram-positive bacteria. The outer membrane in one gram negative bacterium, Roseobacter denitrificans, is a molecular sieve rather than a membrane. Porins cover approximately 70% of the membrane surface and form locally regular lattices (Jarosławski et al., 2009). Artificial channels have been generated by multimerization of beta-strands from natural porin, OmpF of E. coli (Lolicato et al., 2011).