Possible structural role of the disaccharide unit in Fe-bleomycin before and after oxygen activation

Abstract

Our previous investigation of the solution structure of Fe(II)-bleomycin pointed toward the carbamoyl group in the mannose moiety or a water molecule as possible alternative axial ligands to the metal center in this metallo-bleomycin. The possibility of a solvent molecule occupying the apical position trans to the primary amine has not been ruled out yet. In order to explore this possibility even further, the coordination chemistry of azide-bound Fe(II)-bleomycin was investigated with the use of NMR applied to paramagnetic molecules. Fe(II)-and apo-bleomycin were also re-visited. Comparison of the NMR results for both Fe(II)-bound molecules obtained in the present study strongly suggests that the carbamoyl oxygen is ligated to Fe(II), and it is released from coordination upon azide binding. This event is suggested based on the diminished paramagnetic character exhibited by the carbohydrate moiety in Fe(II)-azide-bleomycin when compared with its parent metal complex. A possible structural role for the glucopyranose fragment, which changes throughout the process that starts with metallo-bleomycin formation and ends with DNA binding, is discussed. The study of the coordination of azide by Fe(II)-bleomycin through NMR has not been reported previously. Unlike magnetic CD data, NMR offers a residue-by-residue account of the possible structural changes that take place in Fe(II)-bleomycin after azide binding.

Solution structure of Fe(II)–azide–bleomycin derived from NMR data: transition from Fe(II)–bleomycin to Fe(II)–azide–bleomycin as derived from NMR data and structural calculations

“…The results of these calculations are shown in Tables 3 and 4 for geometries 1 and 2, respectively. These tables show the proton-to-metal distances determined experimentally for FeBLM and FeAZBLM (calculated from T 1 data [19]), and the same proton-to-metal distances measured from the best models for these two compounds. The aforementioned proton-to-metal distances were used to calculate RMSDs that can reflect the differences between the proton-to-metal distances between two particular sets Fig.…”

“…5 Stereo views of FeBLM models 1 and 2 for geometries 1 and 2. These models are the ones that best fit the experimental data collected for FeBLM [19]. The hydrogen atoms have been omitted for clarity of data.…”

“…where H-M is the proton-to-metal distance, for each of the residues in FeBLM and FeAZBLM (bhydroxyhistidine, b-aminoalanine, pyrimidinylpropionamide, methylvalerate, mannose, and gulose) for which T 1 data could be determined [19]. These RMSDs give us an idea of how different the protonto-metal distances between FeBLM and FeAZBLM are from the experimental point of view.…”

“…To gain additional insight into the possible coordination of the carbamoyl group to the Fe(II) center in FeBLM, the Fe(II)-azide-bound BLM (FeAZBLM) complex was studied in our laboratory with the use of NMR spectroscopy [19]. The results of this investigation offer strong evidence that the carbamoyl oxygen is a ligand to the metal center in FeBLM.…”

“…With the aim of supporting or not supporting coordination of a water molecule to the metal center in FeBLM, the solution structure of FeAZBLM has been derived from the NMR data collected for this complex [19]. The structural changes that occur in FeBLM upon azide binding have been monitored by comparing the experimental NMR results with those obtained from the calculated structures in the form of proton-to-metal distance root mean square deviations (RMSDs).…”