Comparison of helix stability in wild-type and mutant LamB signal sequences.
Previous studies of isolated peptides corresponding to the wild-type signal sequence of the LamB protein of Escherichia coli and to several export-impaired mutants demonstrated that a high tendency to adopt an alpha-helical conformation in low dielectric environments was a property of functional sequences. We have now used nuclear magnetic resonance to establish further characteristics of the helical conformation of these signal peptides in a solvent mixture (50% trifluoroethanol, by volume, in water) which mimics the conformational distribution of these peptides in lipid vesicles. The interactions of signal sequences in vivo may depend on the location of the helix in the sequence, on the length of the helical segment, and on the stability of the helix. We find that the hydrophobic core has the most persistent helix conformation and that the stability of this helix correlates with in vivo function of different mutants of the LamB signal sequence. In the family of signal peptides studied here, the length of the helix required for function appears to be less rigidly restricted since a signal peptide from a functional pseudorevertant with 4 residues deleted from the hydrophobic core takes up helix as stably as wild type but incorporates fewer residues in the helix.
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235-9041.
M D
MD
Bruch
L M
LM
Gierasch
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins; D002942:Circular Dichroism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000138:chemical synthesis; D018272:Porins; D011487:Protein Conformation; D021382:Protein Sorting Signals / Q000235:genetics* / Q000378:metabolism; D011991:Receptors, Virus / Q000235:genetics* / Q000378:metabolism
D001425:Bacterial Outer Membrane Proteins; D010455:Peptides; D018272:Porins; D021382:Protein Sorting Signals; D011991:Receptors, Virus; C016532:maltoporins