Semi-automated MicroED system unveils multiple polymorphs in fish-derived guanine crystals

Area of Science:

• Biophysics
• Materials Science
• Crystallography

Background:

• Fish skin structural color is generated by guanine crystals in iridophore cells, arranged in layers to reflect light.
• Guanine crystals' small size and multiple polymorphic forms (α and β) challenge structural characterization.
• Previous studies used powder X-ray diffraction (PXRD) and MicroED, but characterization across fish species remains limited.

Purpose of the Study:

• To establish a semi-automated MicroED system for collecting and processing data from nanoscale guanine crystals.
• To investigate the polymorphic forms of guanine crystals in three fish species: Pacific saury, Pacific cutlassfish, and blue damselfish.
• To validate the system's efficacy for structural determination of submicrometer biogenic crystals.

Main Methods:

• Development of a semi-automated MicroED data collection and processing pipeline.
• Analysis of synthetic guanine crystals under varying pH conditions for system validation.
• MicroED analysis of guanine crystals extracted from Pacific saury, Pacific cutlassfish, and blue damselfish.

Main Results:

• The new system successfully collected and processed MicroED data from guanine crystals.
• Synthetic guanine crystals were characterized, validating the system's performance.
• Both α- and β-polymorphs of guanine were identified in all three analyzed fish species.

Conclusions:

• The developed semi-automated MicroED system is effective for characterizing nanoscale guanine crystals from fish skin.
• The study confirms the presence of both α- and β-guanine polymorphs in Pacific saury, Pacific cutlassfish, and blue damselfish.
• This work advances the structural understanding of biogenic guanine crystals with potential applications in advanced materials.