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Updated: Jul 11, 2026

Assaying for Inorganic Polyphosphate in Bacteria
07:20

Assaying for Inorganic Polyphosphate in Bacteria

Published on: January 21, 2019

Haemophilus influenzae outer membrane protein P5 is associated with inorganic polyphosphate and polyhydroxybutyrate

E Zakharian1, R N Reusch

  • 1Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, USA.

Biophysical Journal
|October 24, 2006
PubMed

Insights

Nontypeable Haemophilus influenzae P5 protein forms cation-selective pores by associating with polyphosphate and poly-(R)-3-hydroxybutyrate. This association explains previously unexplained pore properties in the bacterial outer membrane.

Area of Science:

  • Microbiology
  • Biophysics
  • Structural Biology

Background:

  • Nontypeable Haemophilus influenzae (NTHi) outer membrane protein P5 forms pores with anomalous electrical properties.
  • Discrepancies exist between the theoretical and experimental isoelectric points of NTHi P5, suggesting molecular interactions.

Purpose of the Study:

  • To investigate the molecular basis for the anomalous cation selectivity and reversal potential of NTHi P5 pores.
  • To identify potential interacting molecules that influence NTHi P5 pore function.

Main Methods:

  • Planar lipid bilayer reconstitution assays to study NTHi P5 pore activity.
  • Chemical and immunological analyses to detect associated molecules.
  • Enzymatic treatment with Saccharomyces cerevisiae exopolyphosphatase X to assess polyphosphate involvement.

Main Results:

  • Nontypeable Haemophilus influenzae P5 (NTHi P5) pores exhibited unexpected non-zero reversal potentials and cation selectivity.
  • Chemical analyses identified inorganic polyphosphate (polyP) and poly-(R)-3-hydroxybutyrate associated with NTHi P5.
  • Enzymatic removal of polyP significantly reduced cation selectivity, confirming its role.

Conclusions:

  • NTHi P5 forms large, cation-selective pores through association with polyP and poly-(R)-3-hydroxybutyrate.
  • These polyanionic molecules are crucial for the observed pore properties, resolving previous anomalies.
  • This finding provides new insights into the structure-function relationship of bacterial outer membrane proteins.

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