Protein crystallization by surface entropy reduction: optimization of the SER strategy

Area of Science:

• Protein engineering
• Structural biology
• Biophysics

Background:

• Crystallization is crucial for protein structure determination but challenging for many proteins.
• The surface entropy reduction (SER) method aims to improve protein crystallization by engineering surface residues.
• High-entropy surface residues are often implicated in protein flexibility and poor crystallizability.

Purpose of the Study:

• To systematically compare the efficacy of different residues (Ala, His, Ser, Thr, Tyr) for surface entropy reduction.
• To evaluate the impact of these mutations on protein crystallization propensity.
• To investigate the utility of alternative reservoir solutions, specifically 1.5 M NaCl, for enhanced crystallization screening.

Main Methods:

• Generation of 40 protein mutants by replacing surface residues with high conformational entropy.
• Screening of mutants using standard crystallization procedures.
• Secondary screening of promising mutants using 1.5 M NaCl as a reservoir solution.

Main Results:

• Alanine replacement confirmed as effective for enhancing crystallization.
• Tyrosine and threonine emerged as promising alternative residues for mediating crystal contacts.
• Over 50% of mutants showed improved crystal formation in 1.5 M NaCl solutions, expanding screening conditions.

Conclusions:

• Surface entropy reduction is a powerful strategy for improving protein crystallization.
• Combining surface engineering with diverse screening conditions, including high salt concentrations, maximizes crystallization success.
• This integrated approach offers a robust method for crystallizing challenging proteins.