title: Proteins can convert to beta-sheet in single crystals.
abstract: Raman microscopy was used to follow conformational changes in single protein crystals. Crystals of native insulin and of the 5S and 12S subunits of the enzyme transcarboxylase showed a mixture of Raman marker bands signifying alpha-helix, beta-sheet and nonordered secondary structure. However, by reducing the S-S bonds in the insulin crystal, or by lowering the pH for the 5S crystal, or by soaking substrates into the 12S crystal, the secondary structure in each crystal became predominantly beta-sheet. The beta-form crystals could be dissolved only with difficulty and yielded high-molecular weight protein aggregates, indicating that the beta-sheet formation involves intermolecular contacts. Although their morphology appeared unchanged, the crystals no longer diffracted X-rays. Using crystals that had not been exposed to laser light, the dye thioflavin T formed highly fluorescent complexes with the "beta-transformed" crystals but not with the native crystals.
authors.affiliation: Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: Run
authors.initials: R
authors.lastname: Zheng
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Zheng
authors.forename: Jian
authors.initials: J
authors.lastname: Dong
authors.forename: Paul R
authors.initials: PR
authors.lastname: Carey
mesh_terms: D052160:Benzothiazoles; D019878:Carboxyl and Carbamoyl Transferases / Q000032:analysis / Q000737:chemistry*; D003460:Crystallization; D007328:Insulin / Q000032:analysis / Q000737:chemistry*; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000032:analysis / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013844:Thiazoles / Q000032:analysis / Q000737:chemistry
chemical_list: D052160:Benzothiazoles; D007328:Insulin; D021122:Protein Subunits; D013844:Thiazoles; C009462:thioflavin T; D019878:Carboxyl and Carbamoyl Transferases; C021580:Methylmalonyl-CoA carboxytransferase