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Orientation and effects of mastoparan X on phospholipid bicelles

J A Whiles1, R Brasseur, K J Glover

  • 1Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, USA.

Biophysical Journal
|February 13, 2001
PubMed

Insights

Mastoparan X (MPX) from wasp venom causes cell lysis by increasing membrane permeability. Its orientation differs on zwitterionic versus anionic membranes, suggesting distinct mechanisms for its lytic activity.

Area of Science:

  • Biochemistry
  • Biophysics
  • Molecular Biology

Background:

  • Mastoparan X (MPX) is an ionophoric peptide from wasp venom known to increase cell membrane permeability and cause cell lysis.
  • The exact mechanism of MPX-induced cell lysis, whether through membrane thinning or pore formation, remains debated.

Purpose of the Study:

  • To elucidate the structure and membrane orientation of Mastoparan X (MPX).
  • To investigate how MPX interacts with different membrane compositions, specifically zwitterionic and anionic bicelles.
  • To differentiate between the proposed membrane-thinning and pore-formation mechanisms of MPX lytic activity.

Main Methods:

  • High-resolution and solid-state 2H Nuclear Magnetic Resonance (NMR) techniques were employed.
  • Bicelles, mimicking cell membranes, were used to study MPX association.
  • Nuclear Overhauser Effect Spectroscopy (NOESY) and chemical shift analysis were performed to determine MPX structure and orientation.

Main Results:

  • MPX forms a well-structured amphipathic alpha-helix in bicelles.
  • In zwitterionic bicelles, MPX adopts a perpendicular orientation to the membrane normal, consistent with the 'carpet' mechanism.
  • In anionic bicelles, MPX orients parallel to the membrane normal, supporting the pore model, and significantly disrupts lipid packing.

Conclusions:

  • MPX exhibits distinct membrane association modes depending on lipid charge.
  • The orientation of MPX on zwitterionic membranes aligns with surface-level disruption (carpet mechanism).
  • The longitudinal penetration of MPX into anionic membranes supports a pore-forming mechanism for cell lysis.

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