A visible-light-excited fluorescence method for imaging protein crystals without added dyes

Area of Science:

• Structural Biology
• Biophysics
• Crystallography

Background:

• Fluorescence microscopy is increasingly used for protein crystal detection.
• Current methods rely on UV fluorescence, nonlinear optics, or external dyes.
• A need exists for complementary, non-invasive detection methods.

Purpose of the Study:

• To report a novel visible-light-inducible autofluorescence from protein crystals.
• To demonstrate its utility in protein crystallography and crystal screening.

Main Methods:

• Characterization of visible-light autofluorescence in protein crystals.
• Investigation of fluorescence intensity dependence on temperature and crystal packing.
• Comparison with existing fluorescence microscopy techniques.

Main Results:

• Protein crystals exhibit visible-light autofluorescence due to stabilized conjugated double bonds and charge delocalization.
• Fluorescence intensity increases tenfold at cryogenic temperatures (100 K).
• The method differentiates protein crystals from salt crystals and is suitable for beamline applications.

Conclusions:

• Visible-light autofluorescence offers a complementary, non-damaging method for protein crystal detection.
• The technique is particularly advantageous for cryo-crystallography and crystal identification.
• This autofluorescence provides valuable information for structural biology studies.