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From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
Published on: July 4, 2016
Bacterial Outer Membrane Polysaccharide Export (OPX) Proteins Occupy Three Structural Classes with Selective β-Barrel
Fares Saïdi1,2, Utkarsha Mahanta3, Adyasha Panda3
1Institut National de la Recherche Scientifique (INRS), Centre Armand-Frappier Santé Biotechnologie, Université du Québec, Institut Pasteur International Network, Laval, Quebec, Canada.
Most bacterial outer membrane polysaccharide export (OPX) proteins lack the ability to span the membrane. In Myxococcus xanthus, secretion relies on novel outer membrane beta-barrel porins, termed Wzp, facilitating polysaccharide transport and offering new antimicrobial targets.
Area of Science:
- Microbiology
- Bacterial Cell Biology
- Structural Biology
Background:
- Polysaccharide secretion is crucial for bacterial survival and adaptation.
- Outer membrane polysaccharide export (OPX) proteins are typically involved in translocating polymers across the bacterial envelope.
- The canonical E. coli Wza protein spans the outer membrane via an alpha-helix.
Purpose of the Study:
- To investigate the mechanism of polysaccharide secretion in Myxococcus xanthus.
- To determine the structural and functional roles of OPX homologues in M. xanthus.
- To identify novel components involved in the final step of polysaccharide export across the outer membrane.
Main Methods:
- Comparative genomics of over 91,000 OPX proteins across diverse bacteria.
- Cryo-electron tomography to analyze bacterial cell envelopes.
- Fold recognition and deep learning for structural analysis of M. xanthus proteins.
- Biochemical assays to confirm protein function in polysaccharide translocation.
Main Results:
- Truncated OPX homologues (WzaX/S/B) lacking OM-spanning alpha-helices are common across bacteria.
- Conserved M. xanthus beta-barrel porins (MXAN_7418/3226/1916), designated WzpX/S/B, mediate EPS and MASC export.
- Wzp porin electrostatics correlate with their cognate polymer properties.
- Similar porins are frequently encoded near OPX genes in various bacterial species.
Conclusions:
- A novel secretion paradigm utilizes OPX proteins coupled with outer membrane beta-barrel porins (Wzp) for polysaccharide export.
- This mechanism is widespread across bacteria, particularly for OPX proteins lacking OM-spanning domains.
- Targeting Wzp porins offers a potential strategy for developing new antimicrobials that block polysaccharide export.
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