Plants need to avoid or dissipate excess light energy to protect photosystem II (PSII) from photoinhibitory damage. Higher plants have a conserved system that dissipates excess energy as heat in the light- harvesting complexes of PSII that depends on the transthylakoid ΔpH and violaxanthin de-epoxidase (VDE) activity. To our knowledge, we report the first cloning of a cDNA encoding VDE and expression of functional enzyme in Escherichia coli. VDE is nuclear encoded and has a transit peptide with characteristic features of other lumen-localized proteins. The cDNA encodes a putative polypeptide of 473 aa with a calculated molecular mass of 54,447 Da. Cleavage of the transit peptide results in a mature putative polypeptide of 348 aa with a calculated molecular mass of 39,929 Da, close to the apparent mass of the purified enzyme (43 kDa). The protein has three interesting domains including (i) a cysteine-rich region, (ii) a lipocalin signature, and (iii) a highly charged region. The E. coli expressed enzyme de-epoxidizes violaxanthin sequentially to antheraxanthin and zeaxanthin, and is inhibited by dithiothreitol, similar to VDE purified from chloroplasts. This confirms that the cDNA encodes an authentic VDE of a higher plant and is unequivocal evidence that the same enzyme catalyzes the two-step mono de-epoxidation reaction. The cloning of VDE opens new opportunities for examining the function and evolution of the xanthophyll cycle, and possibly enhancing light-stress tolerance of plants.
Bugos, R. C., & Yamamoto, H. Y. (1996). Molecular cloning of violaxanthin de-epoxidase from romaine lettuce and expression in Escherichia coli. Proceedings of the National Academy of Sciences of the United States of America, 93(13), 6320–6325. https://doi.org/10.1073/pnas.93.13.6320