Protein chemical synthesis by native peptide

ligation Ligation may refer to: * Ligation (molecular biology), the covalent linking of two ends of DNA or RNA molecules * In medicine, the making of a ligature (tie) * Chemical ligation, the production of peptides from amino acids * Tubal ligation, a meth ...

of unprotected

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...

segments is an interesting complement and potential alternative to the use of living systems for producing proteins. The synthesis of proteins requires efficient native peptide ligation methods, which enable the

chemoselective Chemoselectivity is the preferential outcome of a chemical reaction over a set of possible alternative reactions. In another definition, chemoselectivity refers to the selective reactivity of one functional group in the presence of others; often ...

formation of a native

peptide bond In organic chemistry, a peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein cha ...

in aqueous solution between unprotected peptide segments. The most frequently used technique for synthesizing proteins is

Native chemical ligation Native Chemical Ligation (NCL) is an important extension of the chemical ligation concept for constructing a larger polypeptide chain by the covalent condensation of two or more unprotected peptides segments. Native chemical ligation is the most e ...

(NCL). However, alternatives are emerging, one of which is SEA Native Peptide Ligation.

Overview

The SEA group belongs to the ''N,S''-acyl shift systems because its reactivity is dictated by the intramolecular nucleophilic addition of one SEA

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...

group on the C-terminal carbonyl group of the peptide segment. This results in the migration of the peptide chain from the nitrogen to the sulfur. The overall process of SEA native peptide ligation involves first an ''N,S''-acyl shift for in ''in situ'' formation of a peptide

thioester In organic chemistry, thioesters are organosulfur compounds with the functional group . They are analogous to carboxylate esters () with the sulfur in the thioester playing the role of the linking oxygen in the carboxylate ester, as implied by t ...

, and later on, after thiol-thioester exchange, an ''S,N''-acyl shift for formation of the peptide bond.

Description of the reaction

SEA is an abbreviation of ''bis''(2-sulfanylethyl)amido (Scheme 1). SEA ligation involves the reaction of a peptide featuring a C-terminal ''bis''(2-sulfanylethyl)amido group with a Cys peptide. This reaction proceeds probably through the formation of a transient thioester intermediate, obtained by intramolecular attack of one SEA thiol on the peptide C-terminal carbonyl group as shown in Scheme 1. Then, the thioester undergoes a series of thiol-thioester exchanges, including with exogeneous thiols present in the ligation mixture such as mercaptophenyl acetic acid (MPAA). Exchange with the

cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...

thiol group of the second peptide segment results in a transient thioester intermediate, which as for Native Chemical Ligation, rearranges by intramolecular ''S,N''-acyl shift migration into a native peptide bond.

Publication

The first peer reviewed publication describing SEA native peptide ligation was published in ''Organic Letters'' by Melnyk, O. ''et al.'' (Ollivier, N.; Dheur, J.; Mhidia, R.; Blanpain, A.; Melnyk, O., Bis(2-sulfanylethyl)amino native peptide ligation. Org. Lett. 2010, 12, (22), 5238–41; Publication Date (Web): October 21, 2010. A few weeks later, the same reaction was published in the same journal by Liu, C. F (Hou, W.; Zhang, X.; Li, F.; Liu, C. F., Peptidyl N,N-Bis(2-mercaptoethyl)-amides as Thioester Precursors for Native Chemical Ligation. Org. Lett. 2011, 13, 386–389; Publication Date (Web): December 22, 2010).

SEA on/off concept

SEA ^on/off concept exploits the redox properties of SEA group. Oxidation of SEA ^on results in a cyclic disulfide called SEA ^off, which is a self-protected form of SEA ^on. SEA ^off and SEA ^on can be easily interconverted by reduction/oxidation as shown in Scheme 2.

References

{{reflist Peptides Chemical reactions