Association of Spin-Labeled Lipids with β-Barrel Proteins from the Outer Membrane of Escherichia coli

Abstract

The interaction of spin-labeled lipids with beta-barrel transmembrane proteins has been studied by the electron spin resonance (ESR) methods developed for alpha-helical integral proteins. The outer membrane protein OmpA and the ferrichrome-iron receptor FhuA from the outer membrane of Escherichia coli were reconstituted in bilayers of dimyristoylphosphatidylglycerol. The ESR spectra from phosphatidylglycerol spin labeled on the 14-C atom of the sn-2 chain contain a second component from motionally restricted lipids contacting the intramembranous surface of the beta-barrel, in addition to that from the fluid bilayer lipids. The stoichiometry of motionally restricted lipids, 11 and 32 lipids/monomer for OmpA and FhuA, respectively, is constant irrespective of the total lipid/protein ratio. It is proportional to the number of transmembrane beta-strands, eight for OmpA and 22 for FhuA, and correlates reasonably well with the intramembranous perimeter of the protein. Spin-labeled lipids with different polar headgroups display a differential selectivity of interaction with the two proteins. The more pronounced pattern of lipid selectivity for FhuA than for OmpA correlates with the preponderance of positively charged residues facing the lipids in the extensions of the beta-sheet and shorter interconnecting loops on the extracellular side of FhuA.

Molecular simulations and lipid–protein interactions: potassium channels and other membrane proteins

“…This agrees with an estimate of approx. 11 from spin-label studies of OmpA in DMPG (1,2-dimyristoylsn-glycero-3-phosphoglycerol) bilayers [23]. Overall, these simulations present a dynamic picture of lipid-protein interactions, revealing both non-specific and longer-lived, more specific interactions.…”

Redesign of a Plugged β-Barrel Membrane Protein

“…Furthermore, the dynamics of the wildtype FhuA (WT-FhuA) protein at an atomistic level has been revealed by molecular dynamics simulations (35). The FhuA channel exhibits a remarkable robustness, versatility, tractability, and thermal stability, as was well documented by prior spectroscopic and calorimetric studies (22)(23)(24).…”

“…1), which is filled by a globular N-terminal domain (residues 1-160) called the cork (20,21). The barrel has an elliptically shaped cross-sectional area, and the sequential ␤ strands run anti-parallel to one another, conferring an exceptional robustness (22)(23)(24). Adjacent ␤ strands are connected by short turns on the periplasmic side and long loops on the extracellular side (Fig.…”

The Trimeric Periplasmic Chaperone Skp of Escherichia coli Forms 1:1 Complexes with Outer Membrane Proteins via Hydrophobic and Electrostatic Interactions

“…For instance, FhuA displayed selectivity for negatively charged lipids in lipid bilayers, because positive charges dominated in the outer loops near the lipid headgroup region. 40 The loops of NalP have a net charge of + 2, while the turns have a net charge of -3. In the OM, the OMP loops face the negatively charged LPS.…”