The ALDH21 gene found in lower plants and some vascular plants codes for a NADP⁺‐dependent succinic semialdehyde dehydrogenase

Abstract

Lower plant species including some green algae, non-vascular plants (bryophytes) as well as the oldest vascular plants (lycopods) and ferns (monilophytes) possess a unique aldehyde dehydrogenase (ALDH) gene named ALDH21, which is upregulated during dehydration. However, the gene is absent in flowering plants. Here, we show that ALDH21 from the moss Physcomitrella patens codes for a tetrameric NADP -dependent succinic semialdehyde dehydrogenase (SSALDH), which converts succinic semialdehyde, an intermediate of the γ-aminobutyric acid (GABA) shunt pathway, into succinate in the cytosol. NAD is a very poor coenzyme for ALDH21 unlike for mitochondrial SSALDHs (ALDH5), which are the closest related ALDH members. Structural comparison between the apoform and the coenzyme complex reveal that NADP binding induces a conformational change of the loop carrying Arg-228, which seals the NADP in the coenzyme cavity via its 2'-phosphate and α-phosphate groups. The crystal structure with the bound product succinate shows that its carboxylate group establishes salt bridges with both Arg-121 and Arg-457, and a hydrogen bond with Tyr-296. While both arginine residues are pre-formed for substrate/product binding, Tyr-296 moves by more than 1 Å. Both R121A and R457A variants are almost inactive, demonstrating a key role of each arginine in catalysis. Our study implies that bryophytes but presumably also some green algae, lycopods and ferns, which carry both ALDH21 and ALDH5 genes, can oxidize SSAL to succinate in both cytosol and mitochondria, indicating a more diverse GABA shunt pathway compared with higher plants carrying only the mitochondrial ALDH5.

Structural and Biochemical Characterization of Aldehyde Dehydrogenase 12, the Last Enzyme of Proline Catabolism in Plants

“…α-Aminoadipic semialdehyde (AASAL), a substrate analog of GSAL with a 6-carbon chain, is the major substrate of ALDH7 31 and is oxidized at a rate of ~6% compared to GSAL. Succinic semialdehyde, a substrate analog of GRSAL with a 4carbon chain, is the major substrate of ALDH5 and ALDH21 32 . Succinic semialdehyde is oxidized at ~2% rate compared to GSAL.…”

“…ZmALDH12 is NAD + -specific due to presence of the Asp226, whose negatively charged carboxylate side chain likely repels the 2'-phosphate group of NADP + . For comparison, the plant ALDH21 family members, which are NADP + -dependent, have alanine at this position 32 , suggesting that the identity of the residue at this position drives coenzyme preference. To test this hypothesis, the coenzyme preference of the ZmALDH12 D226A mutant was analyzed.…”

NAD+ promotes assembly of the active tetramer of aldehyde dehydrogenase 7A1

“…Initial structural studies revealed ALDH7A1 forms a dimer‐of‐dimers tetramer both in crystallo and in solution . Many other ALDHs form the same tetramer, including ALDH1 , ALDH2 , ALDH5A1 , methylmalonate semialdehyde dehydrogenase , ALDH21 , 2‐aminomuconate‐6‐semialdehyde dehydrogenase , betaine aldehyde dehydrogenase , lactaldehyde dehydrogenase , indole‐3‐acetaldehyde dehydrogenase , α‐ketoglutarate‐semialdehyde dehydrogenase , propionaldehyde dehydrogenase , and salicylaldehyde dehydrogenase . Further investigation of the in‐solution oligomeric state of ALDH7A1 using analytical ultracentrifugation revealed a concentration‐dependent dimer–tetramer equilibrium with a dissociation constant ( K d ) of 16 μ m .…”

3,6-Anhydro-L-Galactose Dehydrogenase VvAHGD is a Member of a New Aldehyde Dehydrogenase Family and Catalyzes by a Novel Mechanism with Conformational Switch of Two Catalytic Residues Cysteine 282 and Glutamate 248

“…EcALDH (24) and most other ALDHs (22,23), the substrate channel and the cofactor channel are always connected throughout the catalytic cycle, which is uninfluenced by the conformational changes of their catalytic residues. In the succinic semialdehyde dehydrogenase PpALDH21 from Physcomitrella patens (25)…”

“…During the catalytic process, these two catalytic residues usually undergo conformational changes, which play a key role in the association/release of the cofactor/substrate/product (19)(20)(21). While the substrate channel and the cofactor channel in most ALDHs are always connected throughout the catalytic cycle (22)(23)(24), the binding of cofactor and/or substrate in some ALDHs results in the two separate channels to be connected due to the conformational change of the catalytic residue Cys (25). In addition to the catalytic residues, the conformational changes of non-catalytic residues in the substrate channel upon the binding of NAD + also induce the connection of two separate channels in the betaine aldehyde dehydrogenase from Staphylococcus aureus (21).…”