Studies on the mode of antifungal action of pradimicin antibiotics. II. D-mannopyranoside-binding site and calcium-binding site.

Abstract

Based on the structure-activity relationship data of BMY-28864 and related pradimicin derivatives, the calcium salt-forming ability and the D-mannopyranoside-speciflc visible absorption maximumshift of BMY-28864 were analysed in the ternary complex formation of BMY-28864 with D-mannopyranoside and calcium. The free C-18 carboxyl group of BMY-28864 was proved to be the sole site for binding to calcium, while no hydroxyl groups of the aglycone were involved in calcium salt formation. The stereospecific D-mannopyranoside-recognizing ability of BMY-28864 was completely abolished by removal of the C-5 disaccharide moiety, and, more particularly, of the C-5 thomosaminemoiety. Close relationship of these findings with the antifungal action was also supported by the in vitro antifungal assay and the potassium leakage induction test.In previous papers1~4), the in vitro antifungal activities of pradimicin and benanomicin derivatives on yeasts were shown to be specifically expressed only in the presence of calcium. Using BMY-28864, a water-soluble pradimicin derivative, specific binding of the pradimicin to yeast cells was proved to depend on the ternary complex formation of BMY-28864with mannan and calcium at a molar ratio of 2 :4 : 15). This highly stereospecific binding of BMY-28864 to the mannose unit (more generally, the specific sugar-recognizing ability of the pradimicin and benanomicin family of antibiotics) is biochemically worth studying, as it is currently unexplicable by the widely accepted concepts of receptor-ligand binding in the light of lectin and carbohydrate sciences. Lectins have been considered to recognize specific sugars based on the intrinsic properties of their peptide components, whereas the pradimicin and benanomicin family of compounds are not peptides. Under these circumstances, it is crucially important and essential to more precisely elucidate the mechanismof ternary complexformation of pradimicins with specific sugars and calcium in critical comparison with lectins. This type of knowledge is not only biochemically useful for receptology, but also clinically important from the viewpoint of selective toxicity of final pradimicin drugs in hosts, as sugars are essential cellular components of host animals to be treated with pradimicin, and assumed to exist ubiquitously at significant concentrations in a variety of forms throughout therapy.In this paper, the structure-activity relationship of BMY-28864 and related pradimicin derivatives is analyzed for identification of the moieties of BMY-28864responsible for binding to D-mannopyranoside and calcium and for induction of the visible absorption maximumshift. In brief, only the free C-18 carboxyl group of BMY-28864serves to bind to calcium as salt, while the C-5 disaccharide moiety is essential for specific recognition of and binding to D-mannopyranoside.

Pradimicin S, a Highly Soluble Nonpeptidic Small-Size Carbohydrate-Binding Antibiotic, Is an Anti-HIV Drug Lead for both Microbicidal and Systemic Use

“…Since no N-glycan deletions have ever been observed in gp41 of PRM-A-resistant (8) and PRM-Sresistant (this study) virus strains, this binding to gp41 may most likely not be directly related to the eventual antiviral activity of the pradimicins. The pradimicins have been suggested to be physiologically active as a (dimeric) complex with Ca 2ϩ (17,29,30). Experimental evidence has indeed been provided that in the presence of PRM-A, (␣-1,2)mannose oligomers, and Ca 2ϩ , a ternary complex is formed that consists of one Ca 2ϩ ion, two pradimicin-A molecules and four (␣-1,2)mannose oligomers (17,29,30).…”

“…In the absence of Ca 2ϩ , PRM-A and PRM-S are unable to bind to HIV-1 gp120 in SPR experiments. Also, methylation of the free carboxylic acid of PRM-A has been demonstrated to result in complete inactivity of the antibiotic (29), suggesting that Ca 2ϩ may act as a bridging ion between the carboxylic acid groups of two PRM-A molecules. It is currently unclear whether Ca 2ϩ solely plays a role in bridging two pradimicin molecules or whether it also plays a role in coordinating mannose binding to the antibiotics, as C-type lectins seem to do.…”

“…MH 193-16F4 (16,20). PRM-A inhibited the growth of fungi (such as Aspergillus) (29) and behaved like the above-mentioned lectins: efficient inhibition of HIV infection and prevention of syncytium formation between persistently HIV-1-infected and uninfected cells (28). Interestingly, we recently could demonstrate that PRM-A, similar to lectins, selects for virus mutants in cell cultures containing deletions in N-glycosylation sites of gp120 (8).…”

“…The pradimicins have been suggested to be physiologically active as a (dimeric) complex with Ca 2ϩ (17,29,30). Experimental evidence has indeed been provided that in the presence of PRM-A, (␣-1,2)mannose oligomers, and Ca 2ϩ , a ternary complex is formed that consists of one Ca 2ϩ ion, two pradimicin-A molecules and four (␣-1,2)mannose oligomers (17,29,30). In the absence of Ca 2ϩ , PRM-A and PRM-S are unable to bind to HIV-1 gp120 in SPR experiments.…”

Candidacidal Action of CF66I, an Antifungal Compound Produced by <i>Burkholderia Cepacia</i>

“…Recent evidences indicated that another mechanism similar to benanomicins and pradimicins may be used to explain the action mode of CF66I against the fungal cell wall. These two drugs killed the fungal cells by damaging the fungal cell wall structure by forming an insoluble complex with polysaccharide (mannan) [12,13]. However, when CF66I was mixed with cell wall polysaccharides, no insoluble complex was observed, but specific binding of CF66I to β-1,6-glucan was observed and its antifungal activity changed, which maybe the reason of CF66I-inducing changes on fungal cell wall.…”