Molecular and structural characterization of the HMP-AB gene encoding a pore-forming protein from a clinical isolate of Acinetobacter baumannii

Curr Microbiol. 2003 Nov;47(5):434-43. doi: 10.1007/s00284-003-4050-4.


The major outer membrane protein of Acinetobacter baumannii is the heat-modifiable protein HMP-AB, a porin with a large pore size allowing the penetration of solutes having a molecular weight of up to approximately 800 Da. Cross-linking experiments with glutardialdehyde failed to show any cross-linking between the monomers, a fact that proves again that this porin protein functions as a monomeric porin. The specific activity of this porin was found to be similar to that of other monomeric porins. Tryptic digestion of the outer membrane yielded a 23-kDa fragment of the HMP-AB protein that was resistant to further trypsin treatment. This observation indicates that HMP-AB is assembled in the membrane in a manner similar to monomeric porins. Cloning of the HMP-AB gene revealed an open reading frame of 1038 bp encoding a protein of 346 amino acids and a calculated molecular mass of 35,636 Da. The amino acid sequence and composition were typical of gram-negative bacterial porins: a highly negative hydropathy index, absence of hydrophobic residue stretches, a slightly negative total charge, low instability index, high glycine content, and an absence of cysteine residues. Sequence comparison of HMP-AB with other outer membrane proteins revealed a clear homology with the monomeric outer membrane proteins, outer membrane protein A (OmpA) of Enterobacteria, and outer membrane protein F (OprF) of Pseudomonas sp. Secondary structure analysis indicated that HMP-AB has a 172-amino acid N-terminal domain that spans the outer membrane by eight amphiphilic beta strands and a C-terminal domain that apparently serves as an anchoring protein to the peptidoglycan layer. The results also indicate that HMP-AB belongs to the eight transmembrane beta-strand family of outer membrane proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acinetobacter baumannii / genetics*
  • Acinetobacter baumannii / physiology*
  • Bacterial Outer Membrane Proteins / genetics
  • Cloning, Molecular
  • Cross-Linking Reagents / pharmacology
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / isolation & purification
  • Genes, Bacterial
  • Glutaral / pharmacology
  • Hydrophobic and Hydrophilic Interactions
  • Molecular Sequence Data
  • Molecular Weight
  • Polymerase Chain Reaction
  • Porins / chemistry
  • Porins / genetics*
  • Porins / isolation & purification
  • Porins / physiology*
  • Protein Structure, Secondary
  • Sequence Analysis, DNA
  • Sequence Analysis, Protein
  • Sequence Homology


  • Bacterial Outer Membrane Proteins
  • Cross-Linking Reagents
  • DNA, Bacterial
  • Porins
  • OMPA outer membrane proteins
  • Glutaral

Associated data

  • GENBANK/AF390104