Evolutionary, Functional and Structural Studies of the ALDH27 Enzymes

Abstract

The ALDH27 family of the aldehyde dehydrogenase superfamily comprises bacterial enzymes poorly studied so far in spite of seemingly being widely distributed, and of their putative important metabolic roles. With the double aim of exploring their occurrence within bacteria and investigating their physiological functions, we performed comprehensive phylogenetic and genomic context analyses. We also biochemically and structurally characterized the three ALDH27 enzymes present in Pseudomonas aeruginosa PAO1 and tested the growth of PAO1 mutant strains on compounds that produce the putative substrate aldehydes. We retrieved 245 non‐redundant ALDH27 sequences from 149 reference genomes, most of them from αβγ‐proteobacteria, some from actinobacteria and a few from firmicutes. These sequences formed two subfamilies: ALDH27A and ALDH27B, which in turn consists of three clades. The neighboring gene of the aldh27A locus is a class I aldolase not characterized so far. Therefore, we could not infer the physiological role of these enzymes from their genomic context. The genomic contexts of the aldh27B1 and aldh27B3 are consistent with their participation in polyamines catabolism. In the neighborhood of the aldh27B2 locus there are genes encoding for either histamine dehydrogenase or histamine‐pyruvate aminotransferase, suggesting their involvement in histamine catabolism. The in vitro and in vivo specificity of PA5312, which belongs to the ALDH27B3 clade, confirmed that it is essential for the catabolism of agmatine, putrescine, cadaverine, spermine, spermidine, and diaminopropane. Similar studies showed that PA0219, which belongs to the ALDH27B2 clade, is essential for the catabolism of histamine. PA4189, which belongs to the ALDH27A subfamily, oxidizes most of the aminoaldehydes substrates of PA5312 and PA0219 enzymes, but they are not its physiological substrates as the PAO1 mutant strain lacking PA4189 activity grew in polyamines or histamine. To find out the structural basis of aldehyde specificity, we obtained the three‐dimensional structures of PA4189 and PA5312 by X‐ray crystallography and performed docking simulations with aldehydes that in vitro are substrates of these enzymes. Then, we examined the conservation within each subfamily and clade of the active site residues in critical positions, and found highly conserved acidic residues, aspartate or glutamate, which may be important for binding the aldehyde substrate. Together, our results provide insights into the diversification of the ALDH27 family in bacteria and of the physiological functions of the members of this family.Support or Funding InformationFinancially supported by DGAPA‐UNAM (PAPIIT IN220317) and CONACYT 283524 grants to RAMC, and DGAPA‐UNAM (PAPIIT IN218819) grant to HRR. ALJV is a recipient of a postdoctoral scholarship from DGAPA‐UNAM and YVCC of a doctoral scholarship from CONACYT.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.