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Periplasmic maltose-binding protein confers specificity on the outer membrane maltose pore of Escherichia coli
Abstract:
ompB mutants of Escherichia coli K-12 are markedly deficient in porin in their outer membrane. This results in a decreased rate of uptake for many substrates: the maltose pore (lambda receptor) can in some circumstances, in the absence of the periplasmic maltose-binding protein, compensate for the consequent defects in permeability to lactose, mannitol, glycylglycyl-L-valine, and tri-L-ornithine. It is postulated that the maltose-binding protein associates with the maltose pore and confers on it the specificity for maltose, and that the absence of the maltose-binding protein leaves the pore open and results in enhanced transmembrane diffusion of molecules other than maltose. This paper presents evidence to support this hypothesis.
Insights
Escherichia coli ompB mutants show reduced outer membrane porins, affecting substrate uptake. The maltose pore, without its binding protein, can enhance diffusion of other molecules, suggesting a regulatory role.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Physiology
Background:
- Outer membrane porins are crucial for nutrient uptake in Escherichia coli.
- ompB mutants exhibit significant porin deficiency, impacting cellular permeability.
- The maltose pore (lambda receptor) plays a role in substrate transport.
Purpose of the Study:
- To investigate the role of the maltose-binding protein in regulating maltose pore function.
- To elucidate the mechanism by which ompB mutants exhibit altered substrate permeability.
- To provide evidence supporting the hypothesis of maltose-binding protein-mediated pore regulation.
Main Methods:
- Analysis of porin expression in ompB mutants of Escherichia coli K-12.
- Assessment of substrate uptake rates for various molecules in wild-type and mutant strains.
- Comparative studies in the presence and absence of the periplasmic maltose-binding protein.
Main Results:
- ompB mutants displayed marked deficiencies in outer membrane porins.
- The maltose pore compensated for permeability defects to certain substrates in the absence of the maltose-binding protein.
- Absence of the maltose-binding protein led to enhanced transmembrane diffusion of non-maltose substrates.
Conclusions:
- The maltose-binding protein is essential for conferring maltose specificity to the maltose pore.
- The absence of the maltose-binding protein results in an 'open' pore state, increasing permeability to other molecules.
- This study supports a model where the maltose-binding protein actively regulates the maltose pore's transport function.