Spectroscopic studies on the interaction of pradimicin BMY-28864 with mannose derivatives

Abstract

Pradimicin BMY-28864 (Pm) is an antibiotic effective against yeasts and fungi, and is known to bind mannose in the presence of Ca2+. We examined spectroscopically the mode of interactions among Pm, Ca2+, and glycosides of mannose and mannose oligosaccharides (Manα-OMe, Manα1-2Manα1-OMe, Manα1-3Manα1-OMe, Manα1-4Manα1-OMe, Manα1-6Manα1-OMe, Manα1-6(Manα1- 3)Manα1-OMe, and Man9GlcNAc2-Asn, a high mannose type N-linked oligosaccharide). All the mannosides interacted with Pm in the presence of Ca2+ and caused absorbance changes. The absorbance changes occurred nonlinearly with respect to the carbohydrate concentration and do not follow a simple binding isotherm equation, suggesting a unique multistep interaction mode. The concentrations that induced half the maximum absorbance change were ~10 mM for the mono- and di-mannosides and around 1.5 mM for the trimannoside and Man9GlcNAc2-Asn. Methyl α-D-glucopyranoside, methyl α- D-galactopyranoside, lactose, and myo-inositol did not affect the absorbance of Pm up to 50 mM. Ca2+ alone also influenced the absorbance of Pm. The absorbance between 200 and 700 nm decreased hypochromically when Ca2+ was added. The concentration that gave half the maximum absorbance decrease caused by Ca2+ was around 15 μM. Our results suggest that two Pm molecules bind one Ca2+, and each Pm binds two mannosyl residues.