Proteins can convert to beta-sheet in single crystals

Area of Science:

• Biophysics
• Structural Biology
• Biochemistry

Background:

• Protein secondary structures, including alpha-helix and beta-sheet, dictate protein function.
• Conformational changes in proteins can lead to altered biological activity and aggregation.
• Raman microscopy offers a non-destructive method to probe molecular structure in biological samples.

Purpose of the Study:

• To investigate conformational changes in single protein crystals using Raman microscopy.
• To identify the secondary structure transformations in insulin and transcarboxylase crystals under various conditions.
• To characterize the structural and physical properties of protein crystals before and after conformational changes.

Main Methods:

• Raman microscopy was employed to analyze the secondary structure of protein crystals.
• Specific treatments were applied: S-S bond reduction for insulin, pH lowering for 5S transcarboxylase, and substrate soaking for 12S transcarboxylase.
• X-ray diffraction and Thioflavin T fluorescence were used to assess crystal integrity and structural changes.

Main Results:

• Native protein crystals exhibited a mix of alpha-helix, beta-sheet, and nonordered structures.
• Treatment induced a shift towards predominantly beta-sheet secondary structure in all tested crystals.
• The beta-sheet transformed crystals were difficult to dissolve, formed aggregates, lost X-ray diffraction ability, and bound Thioflavin T.

Conclusions:

• Specific treatments can induce significant conformational changes in protein crystals, favoring beta-sheet formation.
• Beta-sheet transformation in protein crystals involves intermolecular contacts, leading to aggregation and loss of diffraction.
• Thioflavin T can serve as a marker for this beta-sheet transformation in protein crystals.