An analysis of lamellar x-ray diffraction from disordered membrane multilayers with application to data from retinal...

Area of Science:

• Structural Biology
• Biophysics
• Materials Science

Background:

• Oriented multilayers, such as those in retinal rods, can exhibit both lattice and substitution disorders.
• These disorders complicate the analysis of lamellar X-ray diffraction data.
• Existing methods often fail to account for these combined disorder effects.

Purpose of the Study:

• To develop a generalized analysis for lamellar diffraction from disordered multilayers.
• To quantitatively separate and account for lattice and substitution disorders.
• To derive accurate electron density profiles from complex biological samples like retinal rods.

Main Methods:

• Developed a generalized Patterson function analysis for lattice-disordered multilayers.
• Implemented a recursive procedure using a Gaussian probability model to separate incoherent and coherent intensities.
• Applied the analysis to lamellar X-ray diffraction data from dark-adapted rod outer segments.

Main Results:

• Successfully accounted for and eliminated interference from both lattice and substitution disorders.
• Derived an electron density profile of retinal rod outer segments at 25 Å resolution.
• Quantified the lattice disorder (+/- 19 Å variation) and membrane pair separation disorder (+/- 8 Å variation).

Conclusions:

• The developed analysis method effectively handles complex disorders in multilayered structures.
• Provides accurate electron density profiles essential for understanding biological membrane organization.
• This approach corrects for previously unaccounted-for disorder effects in retinal rod diffraction data.