@article {Hedges2025-az,
	title = {Terminal alkyne formation by a pyridoxal phosphate-dependent enzyme},
	journal = {Nat. Chem. Biol.},
	year = {2025},
	publisher = {Springer Science and Business Media LLC},
	abstract = {Terminal alkyne-containing natural products can undergo the bio-orthogonal {\textquoteright}click{\textquoteright} reaction of Cu(I)-catalyzed azide-alkyne cycloaddition. Recently, an enzymatic mechanism for terminal alkyne formation was discovered in the biosynthesis of L-$\beta$-ethynylserine where the pyridoxal phosphate-dependent enzyme BesB forms a rare terminal alkyne-containing amino acid, L-propargylglycine, from a vinyl halide precursor, 4-chloro-L-allylglycine. Here we present the 1.3-{\AA}-resolution crystal structure of BesB with detailed mechanistic and computational studies. We demonstrate that BesB can reversibly catalyze the exchange of the halogen in various 4-halo-allyl-L-glycines, implying the existence of an allene intermediate, which we then also observe. Taken together, this work supports a mechanism whereby an allene is formed from deprotonation-driven halogen loss and the terminal alkyne is then formed by isomerization of the allene. Our work further expands our understanding of the catalytic repertoire of pyridoxal phosphate-dependent enzymes and will enable development of metal-free allene-forming and alkyne-forming biocatalysts.},
	author = {Hedges, Jason B and Marchand, Jorge A and Calv{\'o}-Tusell, Carla and Wei, Zi-Wang and Millar, Douglas C and Garcia-Borr{\`a}s, Marc and Chang, Michelle C Y and Ryan, Katherine S}
}
