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Identification of the polyamine-induced protein as a periplasmic oligopeptide binding protein
K Kashiwagi1, Y Yamaguchi, Y Sakai
1Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Insights
The polyamine-induced protein (PI protein) in Escherichia coli is identified as a binding protein for an oligopeptide transport system. Its synthesis, stimulated by putrescine, enhances nutrient uptake and promotes cell growth.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Polyamines are essential for cell growth, but their precise roles in nutrient transport are not fully understood.
- A polyamine-requiring mutant of Escherichia coli exhibits stimulated synthesis of a specific protein (PI protein) upon addition of putrescine.
Purpose of the Study:
- To elucidate the physiological function of the polyamine-induced protein (PI protein).
- To investigate the role of PI protein in nutrient transport and its contribution to polyamine-mediated cell growth.
Main Methods:
- Subcellular fractionation to localize PI protein.
- Gene mapping and sequence analysis of the PI protein gene.
- Comparison of PI protein sequence with known oligopeptide binding proteins.
- Measurement of tripeptide transport activity in E. coli mutants.
- Assessment of cell growth in response to oligopeptide vs. amino acid supplementation.
Main Results:
- PI protein was localized to the periplasmic fraction of E. coli cells.
- The gene encoding PI protein was mapped to a chromosomal location associated with oligopeptide transport systems.
- Sequence analysis revealed significant similarity between PI protein and oligopeptide binding proteins from other bacteria.
- Tripeptide transport activity was enhanced in cells grown in the presence of putrescine.
- Oligopeptide supplementation, compared to amino acids, resulted in greater polyamine-stimulated cell growth.
Conclusions:
- The polyamine-induced protein (PI protein) functions as a binding protein within the oligopeptide transport system in E. coli.
- Putrescine stimulates PI protein synthesis, which in turn enhances oligopeptide uptake.
- This enhanced nutrient supply contributes to the overall stimulation of cell growth by polyamines.
Abstract:
The physiological function of the polyamine-induced protein (PI protein), whose synthesis is stimulated at an early stage after the addition of putrescine to growing cells of a polyamine-requiring mutant of Escherichia coli (Mitsui, K., Igarashi, K., Kakegawa, T., and Hirose, S. (1984) Biochemistry 23, 2679-2683), has been studied. The following findings clearly show that the PI protein is a binding protein of an oligopeptide transport system. (a) PI protein was found in a periplasmic fraction. (b) When the restriction map of a clone for the PI protein gene was compared with Kohara's physical map (Kohara, Y., Akiyama, K., and Isono, K. (1987) Cell 50, 495-508), the gene was found at 27 min of the E. coli chromosome, where genes for an oligopeptide transport system were located. (c) The clone contained a 1,629-nucleotide open reading frame encoding a 543-amino acid protein whose calculated Mr was 60,901, and the predicted amino acid sequence from this open reading frame was quite similar to that of an oligopeptide binding protein of Salmonella typhimurium. (d) When the transport activity of a tripeptide, Gly-Leu-125I-Tyr, was measured in a polyamine-requiring mutant of E. coli growing both in the presence and absence of putrescine, the activity was higher in the cells growing in its presence. (e) Polyamine stimulation of cell growth was greater when an oligopeptide rather than corresponding amino acids was added to the medium. These results suggest that the polyamine stimulation of PI protein synthesis at the early stage after the addition of putrescine contributes to the polyamine stimulation of cell growth through the supply of nutrients.