Aldehyde dehydrogenases (ALDHs) comprise a protein superfamily of NAD(P)+-dependent enzymes (EC 1.2.1). The superfamily of plant ALDHs currently contains 13 distinct families. In recent years we kinetically and structurally characterized NAD+-dependent ALDH10 family members from pea (Pisum sativum), maize (Zea mays), tomato (Solanum lycopersicum), ALDH7 family members from maize and pea and ALDH2 family members from maize. The ALDH10 isoforms have been independently shown to oxidize various aminoaldehydes and thus they have been also called aminoaldehyde dehydrogenases or betaine aldehyde dehydrogenases. ALDH7 (EC 1.2.1.31) is also known as a piperideine-6-carboxylate (P6C) dehydrogenase or antiquitin and is primarily involved in the metabolism of lysine. Plant ALDH2 family (EC 1.2.1.3) comprises isoforms catalyzing the oxidation of ethanol-derived acetaldehyde to acetate as well as of other aliphatic and aromatic aldehydes. Some ALDHs from family 2 were originally identified as genes restoring fertility in plants (called RF2A and RF2B), which have the ability to suppress the male-sterile phenotype and restore the production of pollen in maize.
In this work we analyzed enzyme kinetics of ALDH2, ALDH10 and ALDH21 family members from the non-vascular moss Physcomitrella patens, which is a model organism for studies on plant evolution. A single ALDH21 gene is restricted to primitive terrestrial plants including mosses P. patens, Tortula ruralis and the spikemoss Selaginella moellendorffii while it is absent in higher plants. Crystal structures of the ALDH21 apoform and the complexes with the coenzyme and product were solved up to 2.15 Å resolution and revealed the importance of several arginine and tyrosine residues for substrate and coenzyme binding. In particular, Arg 228 functions as a gate to the coenzyme binding site and seals the site upon coenzyme binding.
This work was supported by grant 15-22322S from the Czech Science Foundation and grant IGA_PrF_2016_024 from Palacký University.