Kinetic analysis of lamB mutants suggests the signal sequence plays multiple roles in protein export

• Published in: The Journal of biological chemistry 1986-11, Vol.261 (32), p.15075-15080
• Main Authors: Stader, J, Benson, S A, Silhavy, T J
• Format: Article
• Language: English
• Subjects: Alleles; Amino Acid Sequence; Bacterial Outer Membrane Proteins - genetics; Base Sequence; Biological and medical sciences; Cell physiology; Escherichia coli - genetics; Fundamental and applied biological sciences. Psychology; Molecular and cellular biology; Mutation; Porins; Protein Sorting Signals - genetics; Receptors, Virus - genetics; Secretion. Exocytosis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)66832-2

We have developed a quantitative assay to measure the rate of processing of precursor LamB into mature protein and have used this assay to characterize 10 previously isolated and 3 new lamB signal sequence mutants. The data suggest that the LamB signal sequence serves a complex function. Our assay has revealed five types of signal sequence defect: 1) a strong kinetic defect resulting from alteration of the secondary structure in the putative alpha-helical region in the hydrophobic core, 2) a strong, or 3) a weak kinetic defect due to placement of a charged residue in the hydrophobic core, 4) decreased synthesis of LamB, and 5) both a decrease in synthesis and a strong kinetic defect. The effect of an extragenic suppressor, prlA4 on the rate of processing pLamB containing signal sequence mutations was also examined and compared to the rates in wild-type strains. It was found that prlA4 increases the rate of processing in some, but not all, mutants having a kinetic defect while having no effect on the decreased synthesis seen in mutants of types 4 and 5.