Carbonates are known to exist in natural products, but their biosynthesis has not been linked to any enzymes. An unusual fungal Baeyer-Villiger monooxygenase CcsB is now revealed to catalyze anin-line carbonate formation via a two-step mechanism of oxygen atom insertions.

A novel nitrilase superfamily amidase gene, designated azl13, was cloned from Streptomyces sp. 211726. Bioinformatic and biochemical analysis indicated that Azl13 belongs to a new subfamily in branch 13 of the nitrilase superfamily. His6-Azl13 was expressed in Escherichia coli BL21(DE3) and had the expected molecular mass of 31 kDa, and the enzymatic activity was best at 40°C, pH 8.0. His6-Azl13 had amidase, aryl acylamidase, and acyl transferase activities, and it displayed an unusually wide substrate spectrum. His6-Azl13 was most active on 4-guanidinobutyramide, which is probably its natural substrate, moderately active on short-chain aliphaticamides and weakly active hydrolyzing aromatic and heterocyclic amides. His6-Azl13 also catalyzed acyl transfer to hydroxylamine from acetamide or the herbicide propanil. The substrate spectrum differs from that of the Pseudomonas amidase RamA, probably reflecting high salinity adaptation. The broad substrate spectrum of Azl13 is potentially useful for chemical synthesis and biodegradation.

Gentamicin C complex is a mixture of aminoglycoside antibiotics used to treat severe Gram-negative bacterial infections. We report here key features of the late-stage biosynthesis of gentamicins. We show that the intermediate gentamicin X2, a known substrate for C-methylation at C-6' to form G418 catalyzed by the radical SAM-dependent enzyme GenK, may instead undergo oxidation at C-6' to form an aldehyde, catalyzed by the flavin-linked dehydrogenase GenQ. Surprisingly, GenQ acts in both branches of the pathway, likewise oxidizing G418 to an analogou sketone. Amination of these intermediates, catalyzed mainly by aminotransferase GenB1, produces the known intermediates JI-20A and JI-20B, respectively. Other pyridoxal phosphate-dependent enzymes (GenB3 and GenB4) act in enigmatic dehydroxylation steps that convert JI-20A and JI-20B into the gentamicin C complex or (GenB2) catalyze the epimerization of gentamicin C2a into gentamicin C2.