Molecular and structural characterization of the HMP-AB gene encoding a pore-forming protein from a clinical isolate of Acinetobacter baumannii.
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.
Gribun
Anna
A
Health Sciences Research Center, Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel.
Nitzan
Yeshayahu
Y
Pechatnikov
Izabella
I
Hershkovits
Gitit
G
Katcoff
Don J
DJ
D040981:Acinetobacter baumannii / Q000235:genetics* / Q000502:physiology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D003001:Cloning, Molecular; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004269:DNA, Bacterial / Q000737:chemistry / Q000302:isolation & purification; D005798:Genes, Bacterial; D005976:Glutaral / Q000494:pharmacology; D057927:Hydrophobic and Hydrophilic Interactions; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016133:Polymerase Chain Reaction; D018272:Porins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000502:physiology*; D017433:Protein Structure, Secondary; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D017385:Sequence Homology
D001425:Bacterial Outer Membrane Proteins; D003432:Cross-Linking Reagents; D004269:DNA, Bacterial; D018272:Porins; C078167:OMPA outer membrane proteins; D005976:Glutaral