Structural and Functional Characterization of MppR, an Enduracididine Biosynthetic Enzyme from Streptomyces hygroscopicus: Functional Diversity in the Acetoacetate Decarboxylase-like Superfamily

Abstract

The non-proteinogenic amino acid enduracididine is a critical component of the mannopeptimycins, cyclic glycopeptide antibiotics with activity against drug-resistant pathogens including methicillin-resistant Staphylococcus aureus. Enduracididine is produced in Streptomyces hygroscopicus by three enzymes, MppP, MppQ, and MppR. Based on primary sequence analysis, MppP and Q are pyridoxal-5'-phosphate-dependent aminotransferases; MppR shares low, but significant, sequence identity with acetoacetate decarboxylase. The exact reactions catalyzed by each enzyme, and the intermediates involved in the route to enduracididine are currently unknown. Herein we present biochemical and structural characterization of MppR that demonstrates a catalytic activity for this enzyme and provides clues about its role in enduracididine biosynthesis. Bioinformatic analysis shows that MppR belongs to a previously uncharacterized family within the acetoacetate decarboxylase-like superfamily (ADCSF) and suggests that MppR-like enzymes may catalyze reactions diverging from the well-characterized, prototypical ADCSF decarboxylase activity. MppR shares a high degree of structural similarity with acetoacetate decarboxylase, though the respective quaternary structures differ markedly and structural differences in the active site explain the observed loss of decarboxylase activity. The crystal structure of MppR in the presence of a mixture of pyruvate and 4-imidazolecarboxaldehyde shows that MppR catalyzes the aldol condensation of these compounds and subsequent dehydration. Surprisingly, the structure of MppR in the presence of a mixture of "4-hydroxy-2-ketoarginine" and "2-ketoenduracididine" shows only the correct 4R-enantiomer of "2-ketoenduracididine" bound to the enzyme. These data, together with bioinformatic analysis of MppR homologs, identifies a novel family within the acetoacetate decarboxylase-like superfamily with divergent active site structure and, consequently, biochemical function.

Chemistry and Biology of Teixobactin

“…[19] MppR shares ah igh degree of structurals imilarity with acetoacetate decarboxylase, which converts 1 to 3-[(4R)-2-iminoimidazolidin-4-yl]-2-oxopropanoic acid (2), the ketone form of l-End. [20] The PLP-dependenta minotransferase MppQ then catalyzes the reductivea mination of 2 to produce l-End ( Figure 5). Despite the different stereochemistry at C4, biosynthesis of l-allo-End in teixobactin may follow as imilarr oute to that of l-End.…”

Nicht‐ribosomale Peptidsynthese – Prinzipien und Perspektiven

“…Strukturell noch ungewöhnlicher sind die cyclischen Arg‐Analoga Enduracididin (End), bekannt von Mannopeptimycin, sowie das Capreomycidin (Cap), ein Bestandteil von Peptiden der Tuberactinomycin‐Gruppe wie des Viomycins. Für End wie auch für Cap (Schema a) wird Arg als Ursprung vorgeschlagen. Einiges deutet darauf hin, dass β‐Cyanalanin (Cya) ATP‐abhängig nach einem NRPS‐gebundenen Mechanismus durch Dehydratisierung aus Asn synthetisiert wird .…”

Enduracididine, a rare amino acid component of peptide antibiotics: Natural products and synthesis

“…MppP is a PLP-dependent hydroxylase and catalyses the conversion of L-arginine ( 18 ) and molecular oxygen to 2-oxo-4-hydroxy-5-guanidinovaleric acid ( 20 , Scheme 1) [51]. The enzyme mppR is a pyruvate aldose that catalyses the dehydration/cyclisation of 20 to give cyclic guanidine 21 [52], where transamination by mppQ gives enduracididine ( 1 ). Further transformation to L-β-hydroxyenduracididine ( 5 ) is then catalysed by mppO [52–53].…”

“…The enzyme mppR is a pyruvate aldose that catalyses the dehydration/cyclisation of 20 to give cyclic guanidine 21 [52], where transamination by mppQ gives enduracididine ( 1 ). Further transformation to L-β-hydroxyenduracididine ( 5 ) is then catalysed by mppO [52–53]. …”