The preference of tryptophan for membrane interfaces

Area of Science:

• Biochemistry
• Biophysics
• Membrane Protein Structure

Background:

• Membrane proteins exhibit a preference for tryptophan and tyrosine residues at membrane surfaces.
• This preference is often attributed to enhanced stability via interfacial interactions.
• Existing hypotheses involve amphipathic interactions, hydrogen bonding, and dipole interactions.

Purpose of the Study:

• To investigate the physical basis for tryptophan's preference for membrane surfaces.
• To examine the roles of amphipathic and dipole interactions in this preference.
• To explore alternative explanations for tryptophan's interfacial localization.

Main Methods:

• Utilized 1H magic angle spinning (MAS) chemical shift measurements.
• Employed two-dimensional (2D) nuclear Overhauser effect spectroscopy (2D-NOESY) 1H MAS NMR.
• Applied solid-state 2H NMR to study tryptophan analogues with phosphatidylcholine membranes.

Main Results:

• Tryptophan analogues localized near the glycerol group of phosphatidylcholine membranes.
• The analogues induced similar, modest changes in acyl chain organization.
• Reducing hydrogen bonding or dipole interaction ability did not increase hydrocarbon penetration.

Conclusions:

• Simple amphipathic or dipolar interactions do not explain tryptophan's interfacial preference.
• Tryptophan's flat, rigid shape limits access to the membrane's hydrocarbon core.
• Aromaticity and pi electronic structure likely drive preference for the complex interfacial environment.