Figure 3.

A demonstration of the total numbers of families and protein entries in OMPdb that belong to each of the eight functional categories that we created. There are still a lot of families with β-barrel proteins whose function remains unclear, whereas specific and non-specific channels, together with biogenesis/secretion proteins seem to play a vital role in the bacterial life. Receptors are under-represented in terms of the number of families, but they constitute the second largest category of β-barrel OMPs in absolute numbers of proteins. In general, the largest proportion of outer membrane proteins in Gram-negative bacteria serve as receptors or play a role in biogenesis/secretion. A smaller amount comprises of non-specific channels and adhesion proteins. The category of proteins with unknown function, though it contains a lot of families, has a relatively small number of protein members, which may be due to the progress in whole genome annotation that is being made regarding Gram-negative bacteria.