Total synthesis of horse heart apocytochrome c by conformation-assisted condensation of two chemically synthesized fragments

Quantitative studies of the interactions of metalloproteins with gold nanoparticles: identification of dominant properties of the protein that underlies the spectral changes

The interaction of cytochrome C and a number of its components such as the apo protein, heme and a coordinated iron with gold nanospheres, has been investigated. The role of the heme group and its effect on the observed spectroscopic properties following binding of cytochrome C to the gold surface has been evaluated. Binding of the heme group directly to the gold is not observed, but the presence of the heme group and its effect on the interaction with the metal surface is shown to be influential. Other factors such as the metal oxidation state and the metal-free heme are also studied. A comparison to serum albumin binding as a nonmetallic protein provides further insight into the interaction characteristics.

Synthesis of charybdotoxin and of two N-terminal truncated analogues. Structural and functional characterisation

Charybdotoxin and two N-terminal truncated peptides, corresponding to the 2-37 and 7-37 sequences, were obtained by stepwise solid-phase synthesis using N alpha-t-butyloxycarbonyl and benzyltype side-chain protection. While this strategy was generally useful, the S-acetamidomethyl protecting group used for the six cysteines was not completely stable under HF treatment and its subsequent removal by mercury(II) treatment was neither complete nor devoid of side reactions. The completely deprotected native and truncated sequences were folded efficiently in the presence of glutathione and were finally purified by high-pressure liquid chromatography with overall yields of 4.0-5.0%. Each protein was characterised chemically, structurally and functionally. 1H-NMR spectroscopy was used and a complete assignment of all the protons of the three synthetic proteins was achieved. NMR data show that synthetic charybdotoxin is indistinguishable from the natural protein. The two truncated proteins contain the same elements of secondary structure and a similar overall three-dimensional structure, in agreement with circular dichroic measurements. The shortest analogue, however, may have local structural perturbations and/or higher flexibility. Biological activity on dog epithelial Ca(2+)-activated K+ channels and on rat brain synaptosomal voltage-dependent K+ channels show that synthetic charybdotoxin was as potent as the natural toxin on both channels. For both channels, deletion of the first amino acid, 5-oxoproline (pyroglutamic acid) decreased only slightly the potency of the inhibitor, while deletion of the entire 1-6 segment reduced potency much more. We conclude that the N-terminal region of charybdotoxin plays a functional role in tuning the toxin's biological activity but is not essential for the folding and stability of the structure. The structure of the shortest analogue represents an interesting example of how a well organised and stable alpha/beta fold can be engineered with only 31 amino acid residues.