A divisive role for lipoproteins

Abstract

Most bacterial lipoproteins share a consensus sequence – Leu-Leu-Ala-Gly-Cys – within their signal sequence. The N-acyl-S-sn-1,2-diacylglyceryl lipid modification occurs on the cysteine residue, which also becomes the amino terminus of the mature protein after the action of signal peptidase II. Although the biosynthetic machinery for lipid modification of lipoproteins is essential to bacteria, no single lipoprotein has yet been identified that is essential for viability. Ohara and coworkers1xIdentification and characterization of a new lipoprotein, NlpI, in Escherichia coli K-12. Ohara, M. et al. J. Bacteriol. 1999; 181: 4318–4325PubMedSee all References1 describe a novel lipoprotein in Escherichia coli, NlpI, which might solve this conundrum. A gene interruption within nlpI resulted in a filamentous phenotype when grown in rich media at 42°C. At lower temperatures of 30°C and 37°C, these bacteria are osmotically sensitive for growth. Overexpression of NlpI in media containing radiolabeled palmitic acid or glycerol results in a labeled species at the predicted electrophoretic mobility on SDS-PAGE. Morphologically, NlpI overexpression causes swollen cells and cell pairs. This evidence suggests that the Nlp lipoprotein might be intimately involved in the essential process of cell division. A tandemly repeated tetratricopeptide motif (TPR), commonly used in intermolecular protein interactions, might contribute to the activity of NlpI. The authors point out that a temperature-sensitive truncate might be expressed in their nlpI-interrupted strain and that a complete null mutant will be necessary to show the true, and possibly essential, phenotype of the nlp1 gene.