A new classification of membrane protein crystals

Area of Science:

• Structural Biology
• Biochemistry
• Crystallography

Background:

• The Protein Data Bank (PDB) now contains nearly 700 membrane proteins, enabling meaningful statistical analysis.
• Conventional classification of membrane proteins includes monotopic, β-barrel, and α-helical types.
• Understanding membrane protein crystallization is crucial for structural determination.

Purpose of the Study:

• To analyze the statistical properties of crystallized membrane proteins.
• To investigate the influence of detergent micelle structure on membrane protein crystallization.
• To propose an amended classification for membrane proteins based on crystal packing and detergent arrangement.

Main Methods:

• Statistical analysis of approximately 700 membrane proteins from the Protein Data Bank.
• Classification based on conventional types (monotopic, β-barrel, α-helical) and detergent micelle structure (pockets, filaments, sheets).
• Analysis of crystal packing density, protein mass, oligomerization, space group, and symmetry.

Main Results:

• The conventional classification is appropriate but requires amendment by considering detergent micelle structure.
• Crystal packing density is specific to protein types and detergent arrangements.
• Integral membrane proteins exhibit broader packing density distributions shifted to lower values compared to soluble proteins, not fully explained by solvent expansion.

Conclusions:

• Detergent structure significantly affects membrane protein crystallization.
• A new classification incorporating detergent micelle arrangement provides a refined view of membrane proteins.
• Differences in packing density suggest unique crystallization properties of membrane proteins.