Effects of mutations at glycine residues in the hydrophobic region of the Escherichia coli prolipoprotein signal peptide on the secretion across the membrane.

Each of the 2 glycine residues in the hydrophobic region of the prolipoprotein signal peptide of Escherichia coli was systematically deleted or substituted with a valine residue by oligonucleotide-directed site-specific mutagenesis. Functional analysis of four such mutants as well as four double mutants, resulting from combinations of any two of the single mutations, revealed that (a) glycine residues at positions 9 and 14 could be replaced individually or at the same time with a valine residue without affecting the secretion of prolipoprotein; (b) the deletion of glycine at position 9 had no effect on the secretion of prolipoprotein whereas, when glycine at position 14 was deleted, the glyceride modification and the processing of the mutant prolipoprotein occurred at a much slower rate at 42 degrees C than those of the wild type prolipoprotein; and (c) the effects of deleting glycine at position 14 could be suppressed by the deletion of glycine at position 9, which resulted in shortening the hydrophobic region of the prolipoprotein signal peptide by 2 amino acid residues. These results indicate that the hydrophobic region of the prolipoprotein signal peptide has remarkable flexibility in terms of the relationship between its primary structure and function in protein secretion.