Quantitative Side-Chain Modifications of Methionine-Containing Elastin-Like Polypeptides as a Versatile Tool to Tune Their Properties

Abstract

Tuning the LCST of temperature-responsive recombinant elastin-like polypeptides has usually been achieved by designing different protein sequences, in terms of amino acid composition and length, implying tedious molecular cloning steps. In the present work, we have explored the chemoselective alkylation of methionine as a means to modify elastin repeat side chains and modulate the LCST of the polypeptides.

Tuning Thermoresponsive Properties of Cationic Elastin-like Polypeptides by Varying Counterions and Side-Chains

“…With these new parent ELP samples in hand, we first sought to prepare methyl sulfonium derivatives of ELP-M-20 and ELP-M-40 as analogs of our previously reported methylated (VPGMG) 20 sample, to study the effects of Met sulfonium "dilution" along the ELP backbone on We previously reported that quantitative methylation of Met residues in (VPGMG) 20 led to a complete loss of the Tt due to introduction of multiple hydrophilic sulfonium groups. 23,24 and can also alter the micellization properties of gemini surfactants.…”

“…13 The use of chemoselective reactions to selectively modify specific residues in ELPs post-synthesis has been shown to be a promising means to introduce new functionalities and impart new properties to ELPs, especially at their chain ends, 14,15,16,17 and more scarcely at ELP side-chain residues. 18,19 In a previous study, we reported the chemoselective alkylation of all methionine (Met) residues in the ELP sequence (VPGMG) 20 , which contains Met residues in every repeat, and used this modification to tune the LCST of the resulting polysulfonium ELP derivatives. 20 However, a limitation of this system was the need to use hydrophobic alkylating reagents, i.e.…”

“…The goal of the present work was to improve the versatility of this post-synthesis ELP modification strategy to accommodate a wider range of side-chain functionality, while also being able to retain and tune polysulfonium ELP derivative thermoresponsive properties. 17 To accomplish this goal, we have redesigned ELP sequences to contain fewer Met residues, since the high charge density obtained when sulfonium ions were generated in every pentapeptide repeat in (VPGMG) 20 resulted in very hydrophilic polymers. Decreasing the density of functionalization sites was envisioned to help retain thermoresponsive properties, while also allowing reasonable levels of functional modification.…”

“…20 A variety of epoxide alkylating agents were used for this purpose, which were preferred over the alkyl halides and triflates used previously since many functional epoxides are commercially available or easily synthesized, and epoxides are generally more easily handled than alkyl triflates.…”

Functional Modification of Thioether Groups in Peptides, Polypeptides, and Proteins

“…The multiple Met residues were quantitatively alkylated to give uniform sulfonium derivatives whose properties could be tuned by variation of the alkylating groups. 63 Contrary to the broad applicability of Met alkylation to…”