Identification and characterization of new lipoprotein genes in Escherichia coli K12

　　E.coli lipoproteins are modified with lipids at their N-terminal cysteine residue during the process of translocation across the inner membrane and then localized to either the inner or the outer membrane through the Lol system comprising an ABC transporter (LolCDE)(1), a periplasmic chaperone (LolA)(2) and an outer membrane receptor (LolB)(3). The lipid moieties are required to anchor the protein domains on the periplasmic side of the membrane. Lipoproteins play important roles in many cellular processes including transport of various molecules, cell division and stress response. The whole genome analyses of E.coli K12 suggested that about one hundred species of lipoproteins exist in the cell envelope. However, more than 70 of the predicted lipoprotein genes have not been studied yet.
　　To confirm that be predicted lipoprotein genes code for true lipoproteins, we examined whethere the gene products are labeled with [3H] palmitate and whether their precusor forms are accumulated in the presence of globomycin which inhibits the celevage of lipoprotein signal peptide. 61 lipoproteins were newly identified, indicating that 87 lipoprotein genes are encoded on the chromosome of E.coli K12 at least. In order to define functions of the new lipoproteins, the deletion mutants were constructed by replacing the genes with drug resistance cassettes, and characterized their in vivo phenotypes. Although most of the mutants exhibited no obvious defects, several interesting mutants which show thermosensitive growth at low osmolarity, cell lysis in the stationary phase, hypersensitivity to drugs and abnormal shapes were obtained. Possible functions of new lipoproteins will be discussed.

　　1.Yakushi, T., et al., (2000) Nature Cell Biol., 2, 212
　　2.Matsuyama, S., et al., (1995) EMBO J., 14, 3365
　　3.Matsuyama, S., et al., (1997) EMBO J., 16, 6947