ACORN in CCP4 and its applications.

Area of Science:

• Crystallography
• Structural Biology
• Computational Biology

Background:

• Protein structure determination is crucial for understanding biological function.
• Accurate phase information is essential for solving the crystallographic phase problem.
• Existing phasing methods can be computationally intensive or require specific experimental conditions.

Purpose of the Study:

• To present ACORN, a comprehensive and efficient phasing procedure for protein structure determination.
• To demonstrate the capability of ACORN to derive reliable phases from minimal structural information.
• To showcase the utility of ACORN across different resolution ranges and data types.

Main Methods:

• ACORN utilizes a fragment of the unit cell's scattering matter (less than 5%) to develop phase information.
• The procedure is applicable to atomic resolution data.
• It can also be applied to determine substructures from SAD or MAD data at lower resolutions (e.g., 3.5 A).

Main Results:

• ACORN successfully generated phase information enabling the determination of protein structures.
• A 1093-atom structure was solved using ACORN with data from a single sulfur atom.
• The resulting electron density maps from ACORN typically reveal up to 90% of the complete structure.
• Automated model building was achieved using ARP/wARP or QUANTA with ACORN-derived maps.
• ACORN was successfully used to determine substructures of heavy or anomalous scatterers.
• Four new protein structures were solved by independent users in the UK and France using ACORN.

Conclusions:

• ACORN is a robust and efficient phasing procedure for protein crystallography.
• It significantly simplifies the process of phase determination, even with limited data.
• ACORN facilitates automated model building and structure solution, accelerating structural biology research.