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Outer membrane phospholipase a dimer stability does not correlate to occluded surface area.

Alexandra Ebie Tan1, Karen G Fleming

  • 1T. C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA. Karen.Fleming@jhu.edu

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Membrane protein stability principles remain unclear. Unlike alpha-helical proteins, beta-barrel outer membrane phospholipase A showed no correlation between lost surface area and dimer stability, suggesting van der Waals packing is not a universal predictor.

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Membrane Protein Biophysics

Background:

  • Oligomeric membrane proteins (MPs) are crucial for cellular pathways, but stability principles are poorly understood.
  • Previous studies on alpha-helical MPs (bacteriorhodopsin, glycophorin A) linked lost surface area to stability.
  • It's unknown if this correlation applies to beta-barrel MPs.

Purpose of the Study:

  • To investigate the relationship between interfacial contact surface area and dimer stability in a beta-barrel MP.
  • To determine if van der Waals packing is a general predictor of membrane protein stability.

Main Methods:

  • Created sequence variants of outer membrane phospholipase A (OMPLA) with reduced dimer interface contact area.
  • Used sedimentation equilibrium analytical ultracentrifugation to measure dimerization free energies.
  • Verified variant integrity using specific activity and thermal denaturation assays.

Main Results:

  • No correlation was found between reduced contact surface area and perturbations in OMPLA dimer stability.
  • Findings contradict previous observations in alpha-helical membrane proteins.
  • Structural integrity of variants was confirmed locally.

Conclusions:

  • Van der Waals packing may not be a reliable predictor of stability for all membrane proteins.
  • Oligomer stability in beta-barrel MPs might depend on factors beyond simple surface area contact.
  • Further research is needed to elucidate the principles governing beta-barrel MP stability.