Christin T. Choma

Design of a heme-binding four-helix bundle

The design and characterization of two synthetic peptides that self-assemble into heme-binding proteins are described. The peptides are intended to fold into a four-helix bundle and bind a single heme parallel to the helices in the bundle core using two histidine side chains as ligands. Both proteins bind a single heme in the binding pocket. In one protein there are comparable amounts of low- and high-spin hemes, while in the other low-spin heme predominates. In both proteins, the EPR spectra of the low-spin heme indicate bis-imidazole ligation. The results illustrate that subtle differences in packing, binding pocket flexibility, and ligand orientation can significantly influence the characteristics of functionalized peptides

A general method for coupling unprotected peptides to bromoacetamido porphyrin templates

Abstract An N-terminal cysteine is used to displace bromide from a bromoacetylated porphyrin to yield a thioether linkage between the peptide and the template. Unlike amide coupling reactions, this approach should be compatible with any peptide sequence provided there is only a single cysteine.

Synthesis of hydrophobic peptides: An Fmoc "Solubilising Tail" method

Abstract The development of an Fmoc method for synthesis and purification of hydrophobic peptides using a “solubilising tail” strategy is described. Peptide-constructs of the form hydrophobic peptide-[4-Hmb ester]-solubilising peptide were synthesised. Procedures for forming the 4-Hmb ester linkage, and sequences of solubilising peptides suitable for use with Fmoc SPPS, were investigated. The method was used to synthesise two model peptides and three designed transmembrane peptides.

Synthesis of a designed transmembrane protein by thioether ligation of solubilised segments

Abstract Nα-haloacetylated peptides made by Fmoc solid phase synthesis survived cleavage when EDT was used as a cleavage component. Two segments of a desgned transmembrane protein, one bromoacetylated, the other containing a cysteine, and each bearing a “solubilising tail” peptide, were synthesis by Fmoc SPPS. The two peptides were joined via thioether ligation.

A functional mimic of natural peroxidases: synthesis and catalytic activity of a non-heme iron/peptide hydroperoxide complex

Site-selective attachment of unprotected peptides to a non-heme iron complex is achieved by displacing two halides on the catalyst by peptide caesium thiolates. This coupling approach should be compatible with any peptide sequence provided there is only a single reduced cysteine. The oxidation activity with hydrogen peroxide of the dipeptide–catalyst complex in water is retained, and shows similarities with oxidation mechanisms observed for natural oxidizing enzymes. The results pave the way for the future design of peroxidase mimics where the activity of the catalyst will be modulated by a designed protein matrix.

Synthesis of hydrophobic peptides: An Fmoc “Solubilising Tail” method

Abstract The development of an Fmoc method for synthesis and purification of hydrophobic peptides using a “solubilising tail” strategy is described. Peptide-constructs of the form hydrophobic peptide-[4-Hmb ester]-solubilising peptide were synthesised. Procedures for forming the 4-Hmb ester linkage, and sequences of solubilising peptides suitable for use with Fmoc SPPS, were investigated. The method was used to synthesise two model peptides and three designed transmembrane peptides.

Synthesis of hydrophobic peptides

Abstract The development of an Fmoc method for synthesis and purification of hydrophobic peptides using a “solubilising tail” strategy is described. Peptide-constructs of the form hydrophobic peptide-[4-Hmb ester]-solubilising peptide were synthesised. Procedures for forming the 4-Hmb ester linkage, and sequences of solubilising peptides suitable for use with Fmoc SPPS, were investigated. The method was used to synthesise two model peptides and three designed transmembrane peptides.