You are lost without a map: Navigating the sea of protein structures

Area of Science:

• Biochemistry
• Structural Biology
• Crystallography

Background:

• X-ray crystal structures are crucial for biochemistry research, offering direct answers and inspiring new hypotheses.
• Crystallographic models are interpretations derived from experimental data, not the data itself, posing challenges for non-specialists to assess quality.
• Global measures ensure overall model correctness in the Protein Data Bank (PDB), but do not reveal local feature reliability.

Purpose of the Study:

• To equip users of macromolecular models with tools for critically assessing local model quality.
• To highlight the importance of evaluating the agreement between electron density maps and derived models.
• To guide users in understanding potential misinterpretations, particularly in mobile regions or ligand-bound sites.

Main Methods:

• Review of crystallographic model refinement processes.
• Explanation of the interpretation of electron density maps.
• Provision of illustrated examples of interpreted electron density.

Main Results:

• Global quality measures do not guarantee local model accuracy.
• Misinterpretation of models can occur in regions with poor electron density or high mobility.
• Users need to actively check local agreement between electron density and model for reliable interpretation.

Conclusions:

• Users of crystallographic models must critically evaluate local quality by examining electron density agreement.
• Understanding the interpretive nature of crystallographic models is essential for accurate biochemical research.
• This guide aims to improve the interpretation of structural data, particularly for non-specialists.