title: Structure and binding of peptide-dendrimer ligands to vitamin B12.
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 (K(a)=5.0 x 10(6) M(-1)) and rapidly (k(2)=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)(2)BCD-NH2 leads to stronger (K(a)=12.0 x 10(6) M(-1)) but slower (k(2)=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.
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
authors.forename: Nicolas A
authors.initials: NA
authors.lastname: Uhlich
authors.forename: Antonino
authors.initials: A
authors.lastname: Natalello
authors.forename: Rameshwar U
authors.initials: RU
authors.lastname: Kadam
authors.forename: Silvia M
authors.initials: SM
authors.lastname: Doglia
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Reymond
authors.forename: Tamis
authors.initials: T
authors.lastname: Darbre
mesh_terms: D002942:Circular Dichroism; D050091:Dendrimers / Q000138:chemical synthesis / Q000737:chemistry*; D004058:Diffusion; D008024:Ligands; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D011485:Protein Binding; D017550:Spectroscopy, Fourier Transform Infrared; D014155:Transcobalamins / Q000737:chemistry; D014805:Vitamin B 12 / Q000737:chemistry*
chemical_list: D050091:Dendrimers; D008024:Ligands; D010455:Peptides; D014155:Transcobalamins; D014805:Vitamin B 12