M-4365 G1

Photoactivation of the [3H]dihydrorosaramicin chromophore at a wavelength above 300 nm allows the covalent attachment of the macrolide antibiotic to the bacterial ribosome. Bidimensional electrophoresis shows that the radioactivity is mainly associated with proteins L1, L5, L6, L15, L18, L19, S1, S3, S4, S5 and S9. When photoincorporation of the drug is conducted in the presence of puromycin as effector of [3H]dihydrorosaramicin-binding sites, a decrease in the labeling of most proteins is observed, except for L18 and L19, which are radiolabeled to a larger extent. These results allow us to speculate that L18 and L19 belong to the high-affinity binding site of rosaramicin antibiotic.

Biotransformation of a macrolide antibiotic and a related compound was studied using various macrolide-producing microorganisms grown in the presence of cerulenin, an inhibitor of de novo synthesis of the aglycone moiety. Protylonolide (1) was transformed into 5-O-(4'-O-propionylmycarosyl)protylonolide (2) by a leucomycin-producing strain, Streptoverticillium kitasatoensis KA-429. M-4365 G2 (3) was bioconverted into M-4365 G3 (4), 9-dihydro M-4365 G3 (5), 3-O-acetyl M-4365 G3 (6) and 3-O-acetyl-9-dihydro M-4365 G3 (7) by a spiramycin-producing strain, Streptomyces ambofaciens KA-1028. Forosaminylated derivatives of M-4365 G2 were not obtained using this microorganism. M-4365 G2 was converted into 3-O-acetyl M-4365 G2 (8) by Stv. kitasatoensis strain KA-429 and a carbomycin-producing strain, S. thermotolerans KA-442. These results suggest that the substrate specificity of mycaminose- and forosamine-binding enzymes is high in Stv. kitasatoensis and S. ambofaciens, respectively, while that of the 3-hydroxyl acylating enzyme and mycarose-binding enzyme is low in these microorganisms. The bioconversion products showed lower antibacterial and antimycoplasmal activities than those of M-4365 G2.

The puromycin-induced stimulation of [3H]dihydrorosaramicin binding is due to a twofold increase in affinity of the macrolide antibiotic, with no change in the number of binding sites. Conversely, the binding of [3H]puromycin (A site) is stimulated by rosaramicin. The synergistic effect observed between the two antibiotics can be explained by a conformational change with positive effect, which occurs at the level of their binding sites. Various effectors of [3H]dihydrorosaramicin binding have been tested. Adenosine and dimethyladenosine stimulate the binding; phenylalanine, uridine and gougerotin (A site) have no effect whereas AMP, ADP, ATP, GTP, puromycin 5'-phosphate and lincomycin (P site) are inhibitors. These results point to the importance of the purine moiety in the stimulatory effect and of the phosphate function in reversing this effect. It is concluded that rosaramicin binds to the ribosomal P site and that the synergism observed between rosaramicin and puromycin may be related to interactions between the A and P sites.