Chemical modification of arginine residues of Notechis scutatus scutatus notexin

Fibril formation and toxicity of the non-amyloidogenic rat amylin peptide

Full-length native rat amylin 1-37 has previously been widely shown to be unable to form fibrils and to lack the toxicity of the human amylin form leading to its use as a non-amyloidogenic control peptide. A recent study has suggested that rat amylin 1-37 forms amyloidogenic β-sheet structures in the presence of the human amylin form and suggested that this property could promote toxicity. Using TEM analysis we show here fibril formation by synthetic rat amylin 1-37 and 8-37 peptides when the lyophilized HPLC purified peptides are initially dissolved in 20 mM Tris-HCl. Dissolution of synthetic rat amylin 1-37 and 8-37 peptides in H(2)O or phosphate buffered saline failed to produce fibrils. Addition of 20 mM Tris-HCl to synthetic rat amylin 1-37 and 8-37 peptides initially dissolved in H(2)O also failed to induce fibril formation. The rat amylin fibrils have a uniform structure and bind Congo red suggesting that they are amyloid fibrils. The rat amylin fibrils also bind catalase, which could be inhibited by Amyloid-β 31-35 and a catalase amyloid-β binding domain-like peptide (R9). The rat amylin 1-37 and 8-37 fibrils are toxic in both human pancreatic islet and neuronal cell culture systems. The toxicity of rat amylin fibrils can be inhibited by an amylin receptor antagonist (AC187) and a caspase inhibitor (zVAD-fmk) in a similar manner to previous observations for human amylin toxicity. Chemically induced rat amylin fibril formation of uniform structured fibrils provides a potentially novel anti-amyloid drug discovery tool.

Identifying residues in antigenic determinants by chemical modification

Chemical modification of the side chains of amino acid residues was one of the first methods developed to investigate epitopes in protein antigens. The principle of the method is that alteration of the structure of a key residue of an epitope by a chemical modification will alter reactivity with antibody by affecting either specificity or avidity or both. Chemical modification has the advantage that it can be applied to discontinuous as well as continuous epitopes and may be of value in identifying cryptic epitopes. We consider here the several recent studies that have applied site-specific chemical modification to the identification of epitopes on antigens, including the use of formaldehyde, glutaraldehyde, and acid anhydrides, to produce allergoids where determinants important to reaction with IgE are modified but the ability to elicit an IgG response is retained. It is noteworthy that modification of amino groups with charge reversal appears to be the most useful approach. The approach to the use of site-specific chemical modification as a tool for the study of protein function is discussed, and emphasis is placed on the necessity to (1) validate the specificity of modification and (2) assess potential conformational change that may occur secondary to modification. Finally, a list of chemical reagents used for protein modification is presented, together with properties and references to use.