Windows
Compatible applications
Quick Facts
Basic information about this file format
Extension
.MMCIF
File Type
Macromolecular Crystallographic Information File
Category
Data
Best first step
Use compatible software
Quick Summary
A practical overview of the .mmcif file format
The mmCIF (Macromolecular Crystallographic Information File) format is a standard for representing structural data of biological macromolecules, such as proteins, DNA, and RNA. It was developed by the International Union of Crystallography (IUCr) to overcome the technical limitations of the legacy…
File extension
.MMCIF
File type
Macromolecular Crystallographic Information File
Category
Data
Recommended action
Open with a trusted compatible app
How to open a .mmcif file
Start with a trusted app that supports this format
- Check the file extension carefully and confirm that the file name really ends with .mmcif.
- Use software that supports this file type. If one app does not work, try another compatible program for the same platform.
- Update the application if the file was created by a newer version of the software.
- Scan files from unknown sources before opening them, especially documents, archives, scripts, installers, and executable files.
What is a .mmcif file?
File extension details and usage information
The mmCIF (Macromolecular Crystallographic Information File) format is a standard for representing structural data of biological macromolecules, such as proteins, DNA, and RNA. It was developed by the International Union of Crystallography (IUCr) to overcome the technical limitations of the legacy PDB (Protein Data Bank) format, which featured strict column-width constraints and a maximum limit on the number of atoms and chains it could describe. mmCIF utilizes the Self-defining Text Archive and Retrieval (STAR) syntax, allowing for a highly flexible and extensible dictionary-based structure. This format is now the mandatory standard for depositing structural data into the Worldwide Protein Data Bank (wwPDB) because it can accurately represent massive molecular complexes, such as ribosomes, which exceed the capacity of older formats. Beyond atomic coordinates, mmCIF files store extensive metadata including experimental methods, refinement statistics, chemical descriptions, and biological assembly information. Its machine-readable nature makes it a cornerstone of modern bioinformatics, structural biology, and computational drug discovery, facilitating the automated parsing and analysis of complex three-dimensional biological structures.
Software Compatibility
Programs that may open or work with .mmcif files
macOS
Compatible applications
Linux
Compatible applications
Mobile
Mobile applications
Can .mmcif files be converted?
Options for saving or exporting this file to another format
In many cases, a .mmcif file can be converted by opening it in compatible software and using an option such as Save As, Export, or Convert. The available output formats depend on the file type and the application used.
- Use the original software that created the file when possible.
- Check whether the application supports exporting to common formats.
- Be careful with online converters when working with private, business, or sensitive files.
- If conversion fails, the file may be corrupted, incomplete, encrypted, or not actually a .mmcif file.
Why can't I open a .mmcif file?
Common reasons this file type may not open correctly
Wrong software
The file may require a specific program that supports the .mmcif format.
Incorrect extension
The file extension may have been renamed manually, even though the actual file format is different.
Corrupted file
The file may be incomplete, damaged during download, or transferred incorrectly.
Outdated app
Your software may need to be updated before it can open newer versions of this file format.
Frequently Asked Questions
Common questions about .mmcif files
To open a .mmcif file, use software that supports this file format.
- PyMOL
- UCSF ChimeraX
- VMD
- Jmol
- Mercury
Open the file in compatible software and look for options such as Save As, Export, or Convert. If no export option is available, the file may require a specialized converter or the original application that created it.
- Verify that the file extension is correct.
- Install or update compatible software.
- Try another application that supports this format.
- Check whether the file is corrupted, incomplete, or encrypted.
A file extension alone does not guarantee whether a file is safe or unsafe. Only open files from trusted sources, scan unknown files before opening them, and be especially careful with executable, script, archive, and document files.
File safety tips
Use caution with unknown files
Only open files from trusted sources. Before opening a .mmcif file, scan it with antivirus software, verify that the file extension is expected, and avoid running unknown executable, installer, macro-enabled document, or script files.