Fluorescent bioinspired protein labeling with betalamic acid. Derivatization and characterization of novel protein-betaxanthins

Abstract Betaxanthins are the water-soluble pigments that bestow yellow coloration to fruits, flowers and roots of plants of the Caryophyllales order and present autofluorescence after excitation with blue light. In this work, the semi-synthesis of betaxanthins derived from macromolecules is achieved for the first time by exploiting the reactivity of amine groups belonging to proteins. The synthesis of protein-betaxanthins is demonstrated by spectrophotometry and HPLC-ESI-TOF-MS mass analysis. The derivatization with betalamic acid was in a ratio 1:1 and yielded protein-betaxanthins yellow in color that exhibited fluorescent properties with a maximum excitation wavelength of 476 nm and a maximum emission wavelength of 551 nm. Moreover, staining can be started from purified betalamic acid or directly from raw red beet root extracts. The novel bioinspired labeling reaction allowed protein detection in conventional fluorescence scanning and imaging systems and opens a new perspective for betalamic acid derived molecules as fluorescent probes with multiple biological applications.