Redundant pathways of sunscreen biosynthesis in a cyanobacterium

Route of the sun block: according to empirical evidence, sun-screening mycosporine-like amino acids (MAAs) in Eukarya originate from the shikimic acid pathway, whereas in cyanobacteria, biosynthesis of the MAA shinorine reportedly occurs through the pentose phosphate pathway. However, gene deletion shows that the cyanobacterium Anabaena variabilis ATCC 29143 does not biosynthesise shinorine exclusively by this route.     

A Unique Amino Transfer Mechanism for Constructing the β‐Amino Fatty Acid Starter Unit in the Biosynthesis of the Macrolactam Antibiotic Cremimycin

Cremimycin is a 19‐membered macrolactam glycoside antibiotic based on three distinctive substructures: 1) a β‐amino fatty acid starter moiety, 2) a bicyclic macrolactam ring, and 3) a cymarose unit. To elucidate the biosynthetic machineries responsible for these three structures, the cremimycin biosynthetic gene cluster was identified. The cmi gene cluster consists of 33 open reading frames encoding eight polyketide synthases, six deoxysugar biosynthetic enzymes, and a characteristic group of five β‐amino‐acid‐transfer enzymes. Involvement of the gene cluster in cremimycin production was confirmed by a gene knockout experiment. Further, a feeding experiment demonstrated that 3‐aminononanoate is a direct precursor of cremimycin. Two characteristic enzymes of the cremimycin‐type biosynthesis were functionally characterized in vitro. The results showed that a putative thioesterase homologue, CmiS1, catalyzes the Michael addition of glycine to the β‐position of a non‐2‐enoic acid thioester, followed by hydrolysis of the thioester to give N‐carboxymethyl‐3‐aminononanoate. Subsequently, the resultant amino acid was oxidized by a putative FAD‐dependent glycine oxidase homologue, CmiS2, to produce 3‐aminononanoate and glyoxylate. This represents a unique amino transfer mechanism for β‐amino acid biosynthesis.     

Thermal deactivation and inhibition of D‐Amino acid oxidase in permeabilized cells of the yeast Trigonopsis variabilis

The inhibition of D ‐amino acid oxidase contained in permeabilized cells of the yeast Trigonopsis variabilis by α‐keto acids (pyruvic acid, phenylpyruvic acid and 4‐methylthio‐2‐oxobutanoic acid), products of the transformation of the corresponding D ‐amino acids, was studied. In all cases, inhibition was of the mixed type and significant differences with respect to the inhibition shown by the enzyme from other sources such as pig kidney or the yeast Rhodotorula gracilis were observed. A study was also made of the thermal deactivation of the enzyme contained in permeabilized cells of T variabilis in the temperature range 30–50 °C in sodium phosphate and Tris hydroxylmethyl aminomethane + CaCl₂ buffers. A deactivation mechanism with two steps in series is proposed to account for the variation in activity with time. The results suggest that the enzyme shows greater stability in phosphate buffer, with half‐lives between 7.6 days at 30 °C and 8.6 h at 50 °C. Copyright © 2004 Society of Chemical Industry