TitleKinetic analysis of the assembly of the outer membrane protein LamB in Escherichia coli mutants each lacking a secretion or targeting factor in a different cellular compartment.
Publication TypeJournal Article
Year of Publication2007
AuthorsUreta, AR, Endres, RG, Wingreen, NS, Silhavy, TJ
JournalJ Bacteriol
Date Published2007 Jan
KeywordsBacterial Outer Membrane Proteins, Bacterial Proteins, Carrier Proteins, Cell Membrane, Cytoplasm, Densitometry, Dimerization, Electrophoresis, Polyacrylamide Gel, Escherichia coli, Escherichia coli Proteins, Gene Expression Regulation, Bacterial, Immunoprecipitation, Kinetics, Membrane Transport Proteins, Models, Biological, Mutation, Peptidylprolyl Isomerase, Periplasm, Porins, Protein Folding, Protein Processing, Post-Translational, Protein Sorting Signals, Protein Transport, Receptors, Virus

Outer membrane beta-barrel proteins in gram-negative bacteria, such as Escherichia coli, must be translocated from their site of synthesis in the cytoplasm to the periplasm and finally delivered to the outer membrane. At least a dozen proteins located in the cytoplasm, the periplasm, and both the inner and outer membranes are required to catalyze this complex assembly process. At normal growth temperatures and conditions the transport and assembly processes are so fast that assembly intermediates cannot be detected. Using cells grown at a low temperature to slow the assembly process and pulse-chase analysis with immunodetection methods, we followed newly synthesized LamB molecules during their transit through the cell envelope. The quality and reproducibility of the data allowed us to calculate rate constants for three different subassembly reactions. This kinetic analysis revealed that secB and secD mutants exhibit nearly identical defects in precursor translocation from the cytoplasm. However, subsequent subassembly reaction rates provided no clear evidence for an additional role for SecD in LamB assembly. Moreover, we found that surA mutants are qualitatively indistinguishable from yfgL mutants, suggesting that the products of both of these genes share a common function in the assembly process, most likely the delivery of LamB to the YaeT assembly complex in the outer membrane.

Alternate JournalJ. Bacteriol.