Rapid Catalyst-Free Hydrazone
Ligation: Protein-Pyridoxal
Phosphoramides
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Abstract
Pyridoxal-5′-phosphate (PLP) represents an active
form of
Vitamin B<sub>6</sub> that shows relatively fast imine formation with
hydrazines under physiological conditions without the need of a catalyst.
A convenient phosphate/amine conjugation protocol was developed to
covalently link PLP to proteins, affording proteins capable of hydrazone
formation with bioorthogonal hydrazinyl functional groups. Thus, the
lectin Concanavalin A (Con A) was labeled with PLP. Pretreatment with
fluorescein hydrazide gave dye-labeled Con A that labeled cell surfaces
efficiently. Alternatively, pretargeting was achieved by labeling
cells with Con A-PLP, then treatment in vitro with Alexa Fluor 488
hydrazide