5a2d

Publication Abstract from PubMed

In plants, the last step in the biosynthesis of the osmoprotectant glycine betaine (GB) is the NAD+-dependent oxidation of betaine aldehyde (BAL) catalyzed by some ALDH10 enzymes that exhibit betaine aldehyde dehydrogenase (BADH) activity. Given the irreversibility of the reaction, the short-term regulation of these enzymes is of great physiological relevance to avoid adverse NAD+/NADH ratio decreases. We here report that the Spinacia oleracea betaine aldehyde dehydrogenase ( So BADH) is reversibly and partially inactivated by BAL in the absence of NAD+ in a time- and concentration-dependent mode. Crystallographic evidence indicates that the non-essential Cys450 ( So BADH numbering) forms a thiohemiacetal with BAL, totally blocking the productive binding of the aldehyde. Interestingly, in contrast with Cys450 the catalytic cysteine (Cys291) did not react with BAL in the absence of NAD+. The trimethylammonium group of BAL binds in the same position in the inactivating or productive modes. Accordingly, BAL does not inactivate the C450S So BADH mutant and the degree of inactivation of the A441I and A441C mutants corresponds to their very different ability to bind the trimethylammonium group. Cys450 and the neighboring residues that participate in stabilization of the thiohemiacetal are strictly conserved in plant ALDH10 enzymes with proven or predicted BADH activity, suggesting that inactivation by BAL is a common feature of them. Under osmotic stress conditions, this novel partial and reversible covalent regulatory mechanism may contribute to prevent NAD+ exhaustion, while still permitting the synthesis of high amounts of GB and avoiding the accumulation of the toxic BAL.

Reversible, partial inactivation of plant betaine aldehyde dehydrogenase by betaine aldehyde: mechanism and possible physiological implications.,Zarate-Romero A, Murillo-Melo DS, Mujica-Jimenez C, Montiel C, Munoz-Clares RA Biochem J. 2016 Jan 20. pii: BJ20151084. PMID:26792760^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.