Structure and Binding of Peptide‐Dendrimer Ligands to Vitamin B12 |
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| Authors: | Nicolas A Uhlich Antonino Natalello Rameshwar U Kadam Silvia M Doglia Prof Dr Jean‐Louis Reymond Prof Dr Tamis Darbre Dr |
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| Affiliation: | 1. Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern (Switzerland), Fax: (+41)?31‐631‐8057;2. Department of Biotechnology and Biosciences, University of Milano‐Bicocca, Piazza della Scienza 2, 20126 Milan (Italy), Fax: (+39)?02‐6448‐3565 |
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| Abstract: | The third‐generation peptide‐dendrimer B1 (AcES)8(BEA)4(K‐Amb‐Y)2BCD‐NH2 (B=branching (S)‐2,3‐diaminopropanoic acid, K=branching lysine, Amb=4‐aminomethyl‐benzoic acid) is the first synthetic model for cobalamin‐binding proteins and binds cobalamin strongly (Ka=5.0×106 M ?1) and rapidly (k2=346 M ?1 s?1) by coordination of cobalt to the cysteine residue at the dendrimer core. A structure–activity relationship study is reported concerning the role of negative charges in binding. Substituting glutamates (E) for glutamines (Q) in the outer branches of B1 to form N3 (AcQS)8(BQA)4(B‐Amb‐Y)2BCD‐NH2 leads to stronger (Ka=12.0×106 M ?1) but slower (k2=67 M ?1 s?1) cobalamin binding. CD and FTIR spectra show that the dendrimers and their cobalamin complexes exist as random‐coil structures without aggregation in solution. The hydrodynamic radii of the dendrimers determined by diffusion NMR either remains constant or slightly decreases upon binding to cobalamin; this indicates the formation of compact, presumably hydrophobically collapsed complexes. |
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| Keywords: | dendrimers kinetics protein models thiol ligands vitamin B12 |
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