Two novel cyanobacterial α-dioxygenases for the biosynthesis of fatty aldehydes

Abstract

Abstractα-Dioxygenases (α-DOXs) are known as plant enzymes involved in the α-oxidation of fatty acids through which fatty aldehydes, with a high commercial value as flavor and fragrance compounds, are synthesized as products. Currently, little is known about α-DOXs from non-plant organisms. The phylogenic analysis reported here identified a substantial number of α-DOX enzymes across various taxa. Here, we report the functional characterization and Escherichia coli whole-cell application of two novel α-DOXs identified from cyanobacteria: CalDOX from Calothrix parietina and LepDOX from Leptolyngbya sp. The catalytic behavior of the recombinantly expressed CalDOX and LepDOX revealed that they are heme-dependent like plant α-DOXs but exhibit activities toward medium carbon fatty acids ranging from C10 to C14 unlike plant α-DOXs. The in-depth molecular investigation of cyanobacterial α-DOXs and their application in an E. coli whole system employed in this study is useful not only for the understanding of the molecular function of α-DOXs, but also for their industrial utilization in fatty aldehyde biosynthesis.Key points• Two novel α-dioxygenases from Cyanobacteria are reported• Both enzymes prefer medium-chain fatty acids• Both enzymes are useful for fatty aldehyde biosynthesis Graphical abstract

α‐Dioxygenases (α‐DOXs): Promising Biocatalysts for the Environmentally Friendly Production of Aroma Compounds

“…Very recently, three cyanobacterial α‐DOXs ( Cs DOX from Crocosphaera subtropica , Cal DOX from Calothrix parietina , and Lep DOX from Leptolyngbya sp.) were identified and characterized [2,18b] . This is a significant contribution to the field as Cs DOX, Cal DOX, and Lep DOX are the first prokaryotic α‐DOXs identified so far.…”

“…This is a significant contribution to the field as Cs DOX, Cal DOX, and Lep DOX are the first prokaryotic α‐DOXs identified so far. With the aid of sequence information available in public databases, an unexpected wide distribution of (putative) α‐DOX‐coding sequences across taxonomy ( e. g ., prokaryotes, fungi, and metazoa) could be revealed [18b] . Cyanobacterial α‐DOXs are phylogenetically distinct from plant α‐DOXs with a low sequence identity of around 40 %; however, they share the conserved active site Tyr and two histidine residues as heme ligands, which are essential for α‐DOXs’ oxidative catalysis (Figure 2).…”

“…Collectively, the intrinsic properties of α‐DOX related to its solubility make them industrially incompatible as high cost is posed for biocatalyst production. Consequently, α‐DOXs are best suited for applications in whole‐cell systems (with intact membranes) rather than applying isolated and purified enzymes [15b,18a,b] . α‐DOXs have been operated in resting or growing E. coli cells; Os DOX, for example, successfully converted a series of supplemented SFAs (C 8 to C 16 ) into the corresponding products [15b,18a] .…”

“…The further reduction of overproduced FALs to fatty alcohols is caused by endogenous aldo‐keto reductases (AKRs) and ADHs both acting in the detoxification of reactive aldehydes [6,36a] . However, E. coli cells expressing α‐DOXs displayed reduced or no detectable alcohol formation and this might be attributed to different cell physiologies associated with the redox state of cells, for example [15b,18b] . Besides fatty alcohols, hydroxyl FAs (C n ) can be formed as side‐products due to the peroxidase activities of many α‐DOXs (Figure 1); [32b,37] however, Os DOX does not exhibit peroxidase activity, [33b] qualifying it as a good biocatalyst.…”

“…Among them, α‐DOXs, which are heme‐dependent and act on FAs (C n ) yielding the corresponding FALs (C n‐1 ) and CO 2 , [17a,18] have several advantages including no requirement of cofactors, such as NAD(P)H or redox partner enzymes. Furthermore, they are capable of synthesizing odd‐numbered products [2,15b,18a,b,19] . However, a comprehensive review of α‐DOX as biocatalyst is lacking.…”