Characterisation of YtfM, a second member of the Omp85 family in Escherichia coli.

Omp85 proteins form a ubiquitous protein family, members of which are found in all Gram-negative bacteria. Omp85 of Neisseria meningitidis and YaeT of Escherichia coli are shown to be essential for outer membrane biogenesis. Interestingly, there exists a homologue to YaeT in E. coli and many proteobacteria, denoted YtfM, the function of which has not been described yet. Like YaeT, YtfM is predicted to consist of an amino-terminal periplasmic domain and a membrane-located carboxy-terminal domain. In this study, we present a first characterisation of YtfM by comparison to YaeT concerning structural, biochemical and electrophysiological properties. Furthermore, a knockout strain revealed that ytfM is a non-essential gene and lack of the protein had no effect on outer membrane composition and integrity. The only observable phenotype was strongly reduced growth, indicating an important role of YtfM in vivo.