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Moraxella catarrhalis synthesizes an autotransporter that is an acid phosphatase

Todd C Hoopman1, Wei Wang, Chad A Brautigam

  • 1Department of Microbiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9048, USA.

Journal of Bacteriology
|December 11, 2007
PubMed

Insights

Moraxella catarrhalis synthesizes MapA, a novel outer membrane protein with both acid phosphatase and autotransporter functions. This protein is highly conserved among strains and crucial for the organism's acid phosphatase activity.

Area of Science:

  • Microbiology
  • Protein biochemistry
  • Bacterial pathogenesis

Background:

  • Moraxella catarrhalis is a significant human respiratory pathogen.
  • Autotransporter proteins are a large family of outer membrane proteins involved in bacterial virulence.
  • Acid phosphatases are enzymes that hydrolyze phosphate esters.

Purpose of the Study:

  • To characterize a novel 105-kDa protein from M. catarrhalis O35E with potential acid phosphatase and autotransporter similarities.
  • To determine the function, localization, and conservation of this protein, designated MapA.
  • To investigate the role of MapA in M. catarrhalis acid phosphatase activity.

Main Methods:

  • Bioinformatic analysis (BLAST) to identify protein similarities.
  • Gene cloning and expression in Escherichia coli to confirm enzymatic activity.
  • Cellular fractionation and outer membrane localization studies.
  • Site-directed mutagenesis to identify critical active site residues.
  • Gene inactivation and complementation experiments in M. catarrhalis.
  • Sequence analysis of the mapA gene across multiple strains.

Main Results:

  • A 105-kDa protein, MapA, was identified with significant similarity to bacterial acid phosphatases and autotransporter proteins.
  • MapA possesses acid phosphatase activity, localized to the M. catarrhalis outer membrane.
  • The C-terminal domain of MapA demonstrated translocation ability characteristic of autotransporters.
  • Inactivation of the mapA gene reduced overall acid phosphatase activity in M. catarrhalis.
  • The mapA gene and its encoded protein were found to be highly conserved among tested M. catarrhalis strains.
  • Mutagenesis of a key histidine residue abolished MapA's acid phosphatase activity.

Conclusions:

  • MapA represents the first described autotransporter protein exhibiting acid phosphatase activity.
  • MapA is a conserved, outer membrane-associated enzyme contributing to M. catarrhalis acid phosphatase activity.
  • The dual function of MapA as an enzyme and a potential virulence factor warrants further investigation.

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