Mitogenicity of a lipid-deficient lipoprotein from a mutant Escherichia coli strain

From the mutant bacterial strain Escherichia coli JE5511 lpp lpm, muropeptide-containing and muropeptide-free lipoproteins were prepared. By gas chromatography and by infrared spectroscopy we showed that the products were deficient in the two ester-bound N-terminal fatty acids, but still carried the amide-linked fatty acid. Mutant lipoproteins were tested for mitogenicity in lipopolysaccharide nonresponder C3H/HeJ mice by incorporation of [3H]thymidine and [3H]uridine and by hemolytic plaque assays for immunoglobulin-secreting plasma cells. Our results showed that the mutant lipoproteins still exhibited marked mitogenicity toward mouse B-lymphocytes, although the activity of the products was reduced in comparison to the wild-type lipoprotein. Thus, the presence of one fatty acid in the N-terminal part of lipoprotein is sufficient to bring about mitogenicity.