Haemophilus influenzae Outer Membrane Protein P5 is Associated with Inorganic Polyphosphate and Polyhydroxybutyrate

¹ Univ. of Med. and Dent. of N.J.
² Michigan State University

^* To whom correspondence should be addressed. E-mail: rnreusch{at}msu.edu.

Submitted on August 15, 2006
Revised on August 29, 2006
Accepted on 25 September 2006

	Abstract

Outer membrane protein P5 of nontypeable (acapsulate) Haemophilus influenzae (NTHi P5) forms large, monomeric pores in planar lipid bilayers between symmetric solutions that unpredictably display a non-zero reversal potential. Moreover, NTHi P5 has a high theoretical pI, calculated as 9.58, which is not in agreement with the experimental pI, determined as 6.3 -6.8, or with its preference for cations, disproportionately strong at one side. These anomalous results intimate that NTHi P5 is associated with a polyanion. Chemical and immunological analyses revealed the presence of inorganic polyphosphate (polyP), and the amphiphilic, solvating polyester, poly-(R)-3-hydroxybutyrate (PHB), frequently associated with polyP. A sharp reduction in cation selectivity was observed after addition of Saccharomyces cerevisiae exopolyphosphatase X (scPPX1) to the bilayer, providing functional evidence for the involvement of polyP in selectivity. The results suggest that NTHi P5 associates with polyP and PHB to create large, asymmetric, cation-selective pores in the outer membrane of H. influenzae.

Key Words: NTHi P5, inorganic polyphosphate, outer membrane protein, planar lipid bilayers, poly-(R)-3-hydroxybutyrate, porin

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