An optimized method for 3D fluorescence co-localization applied to human kinetochore protein architecture

Area of Science:

• Cell biology
• Biophysics
• Microscopy

Background:

• Accurate nanoscale measurements are crucial for understanding protein interactions within cells.
• Three-dimensional (3D) fluorescence co-localization offers potential for such measurements.
• Kinetochores are essential structures for chromosome segregation during cell division.

Purpose of the Study:

• To optimize a 3D fluorescence co-localization method for high-accuracy nanoscale measurements.
• To determine the in vivo distance between specific protein epitopes within human kinetochores.
• To investigate the structural state of the Ndc80 complex during metaphase.

Main Methods:

• Optimization of a 3D fluorescence co-localization technique using mean values for chromatic aberration correction.
• Minimizing standard deviations in fluorescence centroid determination, chromatic aberration, and coverslip thickness.
• Computer simulations to assess the impact of parameter variations on measurement accuracy.

Main Results:

• Achieved ~10 nm accuracy in measuring the separation between green and red fluorescently labeled protein epitopes.
• Demonstrated that small standard deviations in key parameters are critical for accurate 3D measurements.
• Found the average protein linkage distance between CENP-A (inner kinetochore) and the Ndc80 complex (outer kinetochore) to be ~90 nm at metaphase.

Conclusions:

• The optimized 3D co-localization method provides high accuracy for nanoscale biological measurements.
• The Ndc80 complex is fully extended at metaphase, with a structure consistent with in vitro crystallographic data.
• This study elucidates the spatial organization of kinetochore components during cell division.