Dear Editor,Outer-membrane protein G (OmpG) is a nonspecific β-barrel porin in the outer membrane of Escherichia coli (E.coli),allowing the passage of ions and molecules up to 900 Da (Fajardo et al.,1998).It comprises of 280 amino acids that form 14-stranded β-sheets with seven long loops (L1-L7) on the extracellular side and six short tums on the periplasmic side (Subbarao and van den Berg,2006;Yildiz et al.,2006;Liang and Tamm,2007).Despite that the OmpG gene exists in the genome of several E.coli strains (Nikaido,1999),expression of OmpG was only observed in E.coli mutants lacking OmpF and LamB (Fajardo et al.,1998) to enable the diffusion of maltodextrins across the bacterial outer membrane.Very interestingly,unlike usual trimeric channel-forming porins,OmpG exhibits fascinating characteristics of a functional monomer in physiological and structural studies (Conlan and Bayley,2003;Mari et al.,2010).Recent atomic force microscopy (AFM) studies showed the dimeric OmpG in lipid,but no evidence shows the physiological relevance of oligomeric forms of OmpG (Mari et al.,2010).The functional monomeric channel porin enables OmpG to be engineered (Bayley et al.,2008) as a single-molecule biosensor (Chen et al.,2008a).