The putative Escherichia coli dehydrogenase YjhC metabolises two dehydrated forms of N-acetylneuraminate produced by some sialidases. Issue 6 (24th June 2020)

• Record Type: Journal Article
• Authors: Kentache, Takfarinas; Thabault, Léopold; Peracchi, Alessio; Frédérick, Raphaël; Bommer, Guido T.; Van Schaftingen, Emile
• Is Part Of: Bioscience reports. Volume 40:Issue 6(2020)
• Publication Date: 2020-06-24
• Subjects: dehydratase -- dehydrogenase -- Escherichia coli -- sialic acid; Molecular biology -- Periodicals; Cytology -- Periodicals; 572.8
• DOI: 10.1042/BSR20200927
• Languages: English
• ISSNs: 0144-8463

Abstract

Abstract: Homologues of the putative dehydrogenase YjhC are found in operons involved in the metabolism of N-acetylneuraminate (Neu5Ac) or related compounds. We observed that purified recombinant YjhC forms Neu5Ac from two dehydrated forms of this compound, 2, 7-anhydro-N-acetylneuraminate (2, 7-AN) and 2-deoxy-2, 3-didehydro-N-acetylneuraminate (2, 3-EN) that are produced during the degradation of sialoconjugates by some sialidases. The conversion of 2, 7-AN into Neu5Ac is reversible and reaches its equilibrium when the ratio of 2, 7-AN to Neu5Ac is ≈1/6. The conversion of 2, 3-EN is irreversible, leading to a mixture of Neu5Ac and 2, 7-AN. NMR analysis of the reaction catalysed by YjhC on 2, 3-EN indicated that Neu5Ac was produced as the α-anomer. All conversions require NAD + as a cofactor, which is regenerated in the reaction. They appear to involve the formation of keto (presumably 4-keto) intermediates of 2, 7-AN, 2, 3-EN and Neu5Ac, which were detected by liquid chromatography-mass spectrometry (LC-MS). The proposed reaction mechanism is reminiscent of the one catalysed by family 4 β-glycosidases, which also use NAD + as a cofactor. Both 2, 7-AN and 2, 3-EN support the growth of Escherichia coli provided the repressor NanR, which negatively controls the expression of the yjhBC operons, has been inactivated. Inactivation of either YjhC or YjhB in NanR-deficient cells prevents the growth on 2, 7-AN and 2, 3-EN. This confirms the role of YjhC in 2, 7-AN and 2, 3-EN metabolism and indicates that transport of 2, 7-AN and 2, 3-EN is carried out by YjhB, which is homologous to the Neu5Ac transporter NanT.