Effects of Hydrophobic Helix Length and Side Chain Chemistry on Biomimicry in Peptoid Analogues of SP-C

Abstract

The hydrophobic proteins of lung surfactant (LS), SP-B and SP-C, are critical constituents of an effective surfactant replacement therapy for the treatment of respiratory distress syndrome. Because of concerns and difficulties associated with animal-derived surfactants, recent investigations have focused on the creation of synthetic analogues of the LS proteins. However, creating an accurate mimic of SP-C that retains its biophysical surface activity is extraordinarily challenging given the lipopeptide's extreme hydrophobicity and propensity to misfold and aggregate. One successful approach that overcomes these difficulties is the use of poly-N-substituted glycines, or peptoids, to mimic SP-C. To develop a non-natural, bioactive mimic of SP-C and to investigate the effects of side chain chemistry and length of the helical hydrophobic region, we synthesized, purified, and performed in vitro testing of two classes of peptoid SP-C mimics: those having a rigid alpha-chiral aromatic helix and those having a biomimetic alpha-chiral aliphatic helix. The length of the two classes of mimics was also systematically altered. Circular dichroism spectroscopy gave evidence that all of the peptoid-based mimics studied here emulated SP-C's secondary structure, forming stable helical structures in solution. Langmuir-Wilhelmy surface balance, fluorescence microscopy, and pulsating bubble surfactometry experiments provide evidence that the aromatic-based SP-C peptoid mimics, in conjunction with a synthetic lipid mixture, have superior surface activity and biomimetic film morphology in comparison to the aliphatic-based mimics and that there is an increase in surface activity corresponding to increasing helical length.

Close mimicry of lung surfactant protein B by “clicked” dimers of helical, cationic peptoids

“…While inclusion of dB1 , mB2 , dB2 , and dB4 led to little to no improvement in adsorptive properties relative to B1 , both mB3 and dB3 enabled a more rapid adsorption of the lipid film, and created surface films that reached a lower γ eq than was seen with the other monomers and disulfide-based dimers. It has been previously shown in peptoid mimics of SP-B that inclusion of aliphatic residues, and in general, an increased proportion of hydrophobicity, facilitated significantly more rapid adsorption to the a/l interface42,44. Of the disulfide-based dimers, dB3 resulted in the lowest γ max and a slightly lower % compression, where the N -propyl chains may once again promote better association with the lipid acyl chains of the dynamic film.…”

Extraordinarily Robust Polyproline Type I Peptoid Helices Generated via the Incorporation of α-Chiral Aromatic N-1-Naphthylethyl Side Chains

“…4 The breadth of peptoid function continues to expand, 5 highlighted by recent investigations that have yielded potent antimicrobial agents, 6,7 modulators of protein-protein interactions, 8-11 RNA-binding agents, 12-15 lung surfactants, 16,17 anti-biofouling agents, 18 asymmetric catalysts, 19 and self-assembled nano-structures. 20,21 Peptoids can be synthesized in a straightforward modular fashion 22 and possess desirable characteristics such as proteolytic stability 23 and increased cellular permeability relative to their α-peptide equivalents.…”

Strategies for Inhibiting Protein Aggregation: Therapeutic Approaches to Protein-Aggregation Diseases

“…Most of the applications of peptoids consist of mimics of a -helices, in two particular areas: antimicrobial agents, where peptoids have been used to mimic a -helical, membrane disruptive peptides (Patch and Barron 2003;Shin et al 2007 ;Gorske and Blackwell 2006 ;Fowler et al 2008 ) , and as mimics of the two hydrophobic a -helical proteins in lung surfactant, SP-B and SP-C (Seurynck- Servoss et al 2006;Brown et al 2008 ) . In the fi eld of protein aggregation, the use of peptoids has been limited to analogues of amylin (islet amyloid polypeptide, IAPP) residues 21-30 (-SNNFGAILSS-).…”