The quaternary structure of Thermus thermophilus aldehyde dehydrogenase is stabilized by an evolutionary distinct C-terminal arm extension

Kevin Hayes,Patricia Armshaw,Mohamed Noor,Ahmed Djeghader,Tewfik Soulimane,Tony Pembroke,Syed Tofail

doi:10.1038/s41598-018-31724-8

Abstract

Aldehyde dehydrogenases (ALDH) form a superfamily of dimeric or tetrameric enzymes that catalyze the oxidation of a broad range of aldehydes into their corresponding carboxylic acids with the concomitant reduction of the cofactor NAD(P) into NAD(P)H. Despite their varied polypeptide chain length and oligomerisation states, ALDHs possess a conserved architecture of three domains: the catalytic domain, NAD(P)+ binding domain, and the oligomerization domain. Here, we describe the structure and function of the ALDH from Thermus thermophilus (ALDHTt) which exhibits non-canonical features of both dimeric and tetrameric ALDH and a previously uncharacterized C-terminal arm extension forming novel interactions with the N-terminus in the quaternary structure. This unusual tail also interacts closely with the substrate entry tunnel in each monomer providing further mechanistic detail for the recent discovery of tail-mediated activity regulation in ALDH. However, due to the novel distal extension of the tail of ALDHTt and stabilizing termini-interactions, the current model of tail-mediated substrate access is not apparent in ALDHTt. The discovery of such a long tail in a deeply and early branching phylum such as Deinococcus-Thermus indicates that ALDHTt may be an ancestral or primordial metabolic model of study. This structure provides invaluable evidence of how metabolic regulation has evolved and provides a link to early enzyme regulatory adaptations.

Highlights

Found in both prokaryotes and eukaryotes, aldehyde dehydrogenases (ALDH) (EC 1.2.1.3) constitute a large family of NAD(P)-dependent enzymes with molecular weights of 50–60 kDa
Through site-directed mutagenesis experiments, it is known that the catalysis occurs as a five-step reaction mediated by three highly-conserved residues Cys[302], Lys[192] and Glu[268], which corresponds to Cys[295], Lys[182] and Glu[261] in ALDH from Thermus thermophilus (ALDHTt)
In the case of ALDHTt, two copies related by a non-crystallographic symmetry (NCS) were present in the asymmetric unit

Summary

Introduction

Found in both prokaryotes and eukaryotes, aldehyde dehydrogenases (ALDH) (EC 1.2.1.3) constitute a large family of NAD(P)-dependent enzymes with molecular weights of 50–60 kDa. In recent times ALDH have become a prime target in cancer research due to the abnormal activity of human ALDH in cancer disease models[6] This group of enzymes has a role in non-enzymatic conditions, such as osmotic stress reduction[7] and mammalian cornea UV exposure protection[8]. Despite the availability of various ALDH superfamily structures (>140 released and >20 unreleased structures), much of the attention has been on mesophilic enzymes including those of human and the archetypal Escherichia coli[10] This is primarily due to their respective multiple roles with non-redundant independent regulation. Recent studies on interesting ALDHs from (hyper) thermophilic bacteria and archaea, including Geobacillus thermodenitrificans[14], Pyrobaculum sp. (PDB ID: 4H73 and 4NMJ) (no primary citation available), Geobacillus thermoglucosidasius (PDB ID: 5J78)[15] and the robustly characterized glyceraldehyde-3-phosphate dehydrogenases from Trichomonas tenax[16] and Sulfolobus solfataricus[17], and the presence of native ALDHTt as a contaminant during T. thermophilus caa3-cytochrome oxidase crystallization[18], motivated us to investigate ALDHTt biochemically and structurally

Methods

Results

Conclusion