An unusual metal-bound 4-fluorothreonine transaldolase from Streptomyces sp. MA37 catalyses promiscuous transaldol reactions

Linrui Wu,Ming Him Tong,Kwaku Kyeremeh,Andrea Raab,Shan Wang,Hai Deng,Qing Fang,Yi Yu

doi:10.1007/s00253-020-10497-z

Abstract

β-Hydroxy-α-amino acids (βH-AAs) are key components of many bioactive molecules as well as exist as specialised metabolites. Among these βH-AAs, 4-fluorothreonine (4-FT) is the only naturally occurring fluorinated AA discovered thus far. Here we report overexpression and biochemical characterisation of 4-fluorothreonine transaldolase from Streptomyces sp. MA37 (FTaseMA), a homologue of FTase previously identified in the biosynthesis of 4-FT in S. cattleya. FTaseMA displays considerable substrate plasticity to generate 4-FT as well as other β-hydroxy-α-amino acids with various functionalities at C4 position, giving the prospect of new chemo-enzymatic applications. The enzyme has a hybrid of two catalytic domains, serine hydroxymethyltransferase (S) and aldolase (A). Site-directed mutagenesis allowed the identification of the key residues of FTases, suggesting that the active site of A domain has a historical reminiscent feature in metal-dependent aldolases. Elemental analysis demonstrated that FTaseMA is indeed a Zn2+-dependent enzyme, the first example of pyridoxal phosphate (PLP) enzyme family fused with a metal-binding domain carrying out a distinct catalytic role. Finally, FTaseMA showed divergent evolutionary origin with other PLP dependent enzymes.

Highlights

Occurring β-hydroxy-α-amino acid residues have been discovered to play important roles as key residues in many bioactive molecules (Jung and Jung 1989).Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Some of β-Hydroxy-α-amino acids (βH-AAs) exist as specialised metabolites (Scott et al 2017)
Some of βH-AAs exist as specialised metabolites (Scott et al 2017)
The fluorinase has been extensively utilised as biocatalyst in generating fluorinated molecule, fluorosalinosporamide (Eustáquio et al 2010) and radiolabelled ligands for positron emission tomography (PET) (Lowe et al 2018; Thompson et al 2014; Zhang et al 2016). 4-Fluorothreonine transaldolase (FTase) is the last enzyme in the pathway that catalyses the biotransformation of

Summary

Introduction

Some of βH-AAs exist as specialised metabolites (Scott et al 2017). Among these βH-AAs, 4-fluorothreonine (4-FT) 1 is the only naturally occurring fluorinated amino acid. The biosynthetic pathway of 1 in S. cattleya has been established as shown in Fig. 1 (O’Hagan and Deng 2014). The hallmark of this biofluorination research is the discovery of the first native fluorination enzyme, fluorinase from S. cattleya, that convert S-adenosyl-L-methionine and fluoride ion to generate 5′-fluoro-5′-deoxy-adenosine (5′-FDA) and Lmethionine (Deng et al 2004; O’Hagan et al 2002). The fluorinase has been extensively utilised as biocatalyst in generating fluorinated molecule, fluorosalinosporamide (Eustáquio et al 2010) and radiolabelled ligands for positron emission tomography (PET) (Lowe et al 2018; Thompson et al 2014; Zhang et al 2016). 4-Fluorothreonine transaldolase (FTase) is the last enzyme in the pathway that catalyses the biotransformation of

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Conclusion