title: Systematic modulation of Michael-type reactivity of thiols through the use of charged amino acids.
abstract: A quantitative structure-reactivity relationship for the Michael-type addition of thiols onto acrylates was determined. Several thiol-containing peptides were investigated by examining the correlation between the second-order rate constant of their addition onto PEG-diacrylate and the pK(a) of the thiols within a peptide. By introducing charged amino acids in close proximity to a cysteine, the pK(a) of the thiol was systematically modulated by electrostatic interactions. Positive charges from the amino acid arginine decreased the pK(a) of the thiol and accelerated the reaction with acrylates while negative charges from aspartic acids showed the opposite effect. A linear correlation between thiolate concentrations and kinetic constants was found, confirming the role of thiolates as the reactive species in this Michael-type reaction. The relevant factors influencing the reactivity were the sign and the number of the neighboring charges, while the position of these charges had little effect on reactivity. These results provide a basis for the rational design of peptides, where the kinetics and thus selectivity of protein/peptide conjugation with polymeric structures via Michael-type addition reactions can be controlled.
authors.affiliation: Department of Materials and Institute for Biomedical Engineering, ETH Zurich and the University of Zurich, Zurich, Switzerland.
authors.forename: M P
authors.initials: MP
authors.lastname: Lutolf
authors.forename: N
authors.initials: N
authors.lastname: Tirelli
authors.forename: S
authors.initials: S
authors.lastname: Cerritelli
authors.forename: L
authors.initials: L
authors.lastname: Cavalli
authors.forename: J A
authors.initials: JA
authors.lastname: Hubbell
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D015195:Drug Design; D007700:Kinetics; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D010455:Peptides; D013438:Sulfhydryl Compounds; D011092:Polyethylene Glycols