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Identification and localization of Myxococcus xanthus porins and lipoproteins

Swapna Bhat1, Xiang Zhu, Ricky P Patel

  • 1Department of Microbiology, University of Georgia, Athens, Georgia, United States of America.

Plos One
|December 2, 2011
PubMed

Insights

Myxococcus xanthus DK1622 outer membrane proteins, including Oar porin, were identified using computational predictions and LC-MS/MS. Specific amino acid sequences were found to direct lipoproteins to inner, outer, or extracellular locations.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Biochemistry

Background:

  • Myxococcus xanthus DK1622 possesses inner and outer membranes (IM/OM) separated by peptidoglycan.
  • Integral membrane β-barrel proteins in the OM form pores crucial for transport and signaling, like the C-signal porin Oar.
  • Lipoproteins, anchored by lipids, are found in IM, OM, and extracellular compartments (ECM).

Purpose of the Study:

  • To evaluate computational programs for identifying β-barrel proteins in M. xanthus.
  • To identify and characterize OM β-barrel proteins and lipoproteins in M. xanthus.
  • To investigate the sorting mechanisms of lipoproteins to specific cellular compartments.

Main Methods:

  • Computational prediction using Signal P, Lipo P, TMHMM, TMBETA-SVM, and TMBETADISC-RBF.
  • Sucrose density gradients for IM/OM fractionation.
  • Liquid chromatography-tandem mass spectrometry (LC-MS/MS) for protein identification.
  • Site-directed mutagenesis and immuno transmission electron microscopy.

Main Results:

  • Combined computational tools accurately predicted β-barrel proteins, with 228 identified (3.1% of genes).
  • LC-MS/MS identified 54 β-barrel proteins in the OM and 44 predicted lipoproteins.
  • Specific N-terminal sequences, particularly alanine at +7 for ECM and lysine at +2 for IM, direct lipoprotein localization, with alanine at +7 being essential for FibA ECM sorting.

Conclusions:

  • Accurate prediction of M. xanthus β-barrel proteins requires integrated computational approaches.
  • Lipoprotein localization is governed by N-terminal sorting sequences, with distinct signals for IM, OM, and ECM.
  • ECM lipoprotein secretion utilizes a unique mechanism, allowing targeted protein delivery by manipulating amino acid sequences.

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