Effect of Peptide Sequence on the LCST-Like Transition of Elastin-Like Peptides and Elastin-Like Peptide–Collagen-Like Peptide Conjugates: Simulations and Experiments

Abstract

Elastin-like polypeptides (ELPs) are thermoresponsive biopolymers that undergo an LCST-like phase transition in aqueous solutions. The temperature of this LCST-like transition, T t , can be tuned by varying the number of repeat units in the ELP, sequence and composition of the repeat units, the solution conditions, and via conjugation to other biomacromolecules. In this study, we show how and why the choice of guest (X) residue in the VPGXG pentad repeat tunes the T t of short ELPs, (VPGXG) 4 , in the free state and when conjugated to collagen-like peptides (CLPs). In experiments, the (VPGWG) 4 chain (in short, WWWW) has a T t < 278 K, while (VPGFG) 4 or FFFF has a T t > 353 K in both free ELP and ELP−CLP systems. The T t for the FWWF ELP sequence decreases from being >353 K for free ELP to <278 K for the corresponding ELP−CLP system. The decrease in T t upon conjugation to CLP has been shown to be due to the crowding of ELP chains that decreases the entropic loss upon ELP aggregation. Even though the net hydrophobicity of ELP has been reasoned to drive the T t , the origins of lower T t of WWWW compared to FFFF are unclear, as there is disagreement in hydrophobicity scales in how phenylalanine (F) compares to tryptophan (W). Motivated by these experimental observations, we use a combination of atomistic and coarse-grained (CG) molecular dynamics simulations. Atomistic simulations of free and tethered ELPs show that WWWW are more prone to acquire β-turn structures than FFFF at lower temperatures. Also, the atomistically informed CG simulations show that the increased local stiffness in W than F due to the bulkier side chain in W compared to F, alone does not cause the shift in the transition of WWWW versus FFFF. The experimentally observed lower T t of WWWW than FFFF is achieved in CG simulations only when the CG model incorporates both the atomistically informed local stiffness and stronger effective attractions localized at the W position versus the F position. The effective interactions localized at the guest residue in the CG model is guided by our atomistically observed increased propensity for β-turn structure in WWWW versus FFFF and by past experimental work of Urry et al. quantifying hydrophobic differences through enthalpy of association for W versus F.

Thermal Compaction of Disordered and Elastin-like Polypeptides: A Temperature-Dependent, Sequence-Specific Coarse-Grained Simulation Model

“…ELPs undergo a sharp solubility transition at lower critical solution temperature (LCST) from solvated phases at temperatures below to coacervates at temperatures above. The transition temperature, often referred to and measured as the cloud point T c , depends most notably on sequence length (molecular weight), concentration of ELPs, and the identity of the guest residue X [18][19][20][21][22][23][24][25][26][27][28] . Strongly hydrophobic guest residues result in typically low T c 21 .…”

Fine structural tuning of the assembly of ECM peptide conjugates via slight sequence modifications

“…The formation of these structures is mediated by the thermally mediated phase separation of the ELP domain in the center of a bilayer-like structure, with triple-helical CLP domains at the surfaces of the bilayer. While conjugates comprising a (VPGFG) 6 domain chemically attached to the N-terminal end of CLP domains of different lengths and compositions uniformly adopted thermoresponsive vesicular structures, a set of (VPGXG) 4 -(GPO) 8 bioconjugates (with X comprising W or F) were demonstrated to assemble into bilayer, platelet-like morphologies, although lacked thermoresponsiveness ( 23 , 27 ). On the basis of these results, we sought to establish that the fine level of control in the compositions and lengths of these peptide-based, thermally triggered amphiphiles would serve as a sensitive handle for generating collagen-binding nanostructures with different morphologies and thermal responsiveness.…”

Recent trends in protein and peptide-based biomaterials for advanced drug delivery

“…Temperature -triggered self-assembly of CLPs : Kiick and co-workers recently reported the temperature -triggered self-assembly of CLP-hybrid materials [ [261] , [262] , [263] , [264] ]. They appended a synthetic polymer, poly(diethylene glycol methyl ether methacrylate) (PDEGMEMA) or human tropoelastin -derived elastin-like polypeptide (ELP, to be discussed in a later section) with CLPs.…”