Orchestration of Structural, Stereoelectronic, and Hydrogen-Bonding Effects in Stabilizing Triplexes from Engineered Chimeric Collagen Peptides (Pro^X-Pro^Y-Gly)₆ Incorporating 4(R/S)-Aminoproline

Abstract

Collagens are an important family of structural proteins found in the extracellular matrix with triple helix as the characteristic structural motif. The collagen triplex is made of three left-handed polyproline II (PPII) helices with each PPII strand consisting of repetitive units of the tripeptide motif X-Y-Gly, where the amino acids X and Y are most commonly proline (Pro) and 4R-hydroxyproline (Hyp), respectively. A C4-endo pucker at X-site and C4-exo pucker at Y-site have been proposed to be the key for formation of triplex, and the nature of pucker is dependent on both the electronegativity and stereochemistry of the substituent. The present manuscript describes a new class of collagen analogues-chimeric cationic collagens-wherein both X- and Y-sites in collagen triad are simultaneously substituted by a combination of 4(R/S)-(OH/NH2/NH3(+)/NHCHO)-prolyl units and triplex stabilities measured at different pHs and in EG:H2O. Based on the results a model has been proposed with the premise that any factors which specifically favor the ring puckers of C4-endo at X-site and C4-exo at Y-site stabilize the PPII conformation and hence the derived triplexes. The pH-dependent triplex stability uniquely observed with ionizable 4-amino substituent on proline enables one to define the critical combination of factors C4-(exo/endo), intraresidue H-bonding, stereoelectronic (R/S) and n → π* interactions in dictating the triplex strength. The ionizable NH2 substituent at C4 in R/S configuration is thus a versatile probe for delineating the triplex stabilizing factors and the results have potential for designing of collagen analogues with customized properties for material and biological applications.

Stereodependent and solvent‐specific formation of unusual β‐structure through side chain‐backbone H‐bonding in C4(S)‐(NH2/OH/NHCHO)‐L‐prolyl polypeptides

“…The peptides (4 S ) ‐Amp 9 ( P2 ) and (4 S )‐ Hyp 9 ( P5 ) after purification were treated with acetic anhydride/ N,N ‐diisopropylethylamine (DIPEA) in DMF to afford the C4( S )‐O/N‐acetylated peptides (4 S )‐ acHyp 9 ( P6 ) and (4 S )‐ acAmp 9 ( P7 ). The peptide (4 S )‐ fAmp 9 ( P8 ) was synthesized from N1‐(Fmoc)−4‐formamido proline . The peptides, (4 R )‐ Amp 9 ( P1 ) and (4 S )‐ Amp 9 ( P2 ), synthesized on MBHA resin using t Boc strategy with N1‐( t‐ Boc)−4( R / S )NH‐(Fmoc)‐aminoproline were guanidinylated as reported earlier .…”

“…Figure illustrates the possible structures of C4( S )‐substituted polypeptides (X = O, NH, NCHO) in water and TFE. The PPII structure (Figure A) in water maximizes all favorable interactions C4‐ endo pucker, gauche effect, n→π* interaction and intraresidue (C4)‐NH 2 —OC‐(C2) H‐bond. The classical β‐structure in peptides arises from reciprocal H‐bonding among the backbone amides of two polypeptide chains.…”

Comparative effects of trifluoromethyl- and methyl-group substitutions in proline

“…In each individual case, changes resulting from the substitution of a Pro with an analogue were attributed to structural differences or are rationalized using data obtained from experimental molecular models. [29][30][31][32] Parallel to these efforts, significant computational data have been generated for select ProAs in recent literature. [33][34][35][36][37][38] Curiously, the majority of the characterized substitution effects have involved very closely related ProAs and typically these substitutions occupied position 4 of the ring.…”

Promotion of the collagen triple helix in a hydrophobic environment

“…Nonetheless, these peptides usually contain additional ionisable, polar, metal coordinating and other functional groups that are not significantly hydrophobic. 13,14 The modifications aim to manipulate, preferably enhance, the stability of the triple helix formed by CMPs, 15,16 drive their high-order self-assembly, 17,18 or otherwise enable the use of CMPs as a scaffold for functionalization. 19,20 As an alternative approach to manipulate the stability of the collagen structure, there are modifications which impact the nucleation of the triple helix.…”