Flexible fitting of high-resolution x-ray structures into cryoelectron microscopy maps using biased molecular...

Area of Science:

• Structural biology
• Biophysics
• Computational biology

Background:

• Cryoelectron microscopy (cryo-EM) provides low-resolution structural information.
• Accurately fitting high-resolution atomic models into these maps remains challenging.
• Protein structures often undergo conformational changes during biological activity.

Purpose of the Study:

• To develop a flexible fitting methodology for all-atom structures into low-resolution cryo-EM maps.
• To enhance the accuracy of structural model fitting using molecular dynamics.
• To enable reliable determination of protein conformations from cryo-EM data.

Main Methods:

• Simulated flexibility using classical molecular dynamics.
• Introduced an effective potential proportional to the correlation coefficient between experimental and synthetic maps.
• Calculated forces as the gradient of the correlation coefficient to guide molecular dynamics.
• Tested on five proteins with known conformational changes and experimental cryo-EM data of elongation factor G.

Main Results:

• Achieved high-accuracy fitting of all-atom structures into cryo-EM maps.
• Demonstrated successful modeling of conformational transitions in test proteins.
• Obtained results comparable to previous studies for elongation factor G.
• Showed that correlation coefficient and secondary structure preservation can avoid overfitting.

Conclusions:

• The developed method enables accurate flexible fitting of all-atom models into low-resolution cryo-EM maps.
• The approach effectively captures protein conformational dynamics relevant to biological function.
• This methodology provides a reliable tool for structural analysis using cryo-EM data.