(15c) Investigating Sequence Effects on the Biodegradation of Peptoid Substrates

The structure and function of biological molecules arise from the precise sequence of building blocks responsible for encoding their properties. Nature’s strategy for structure-property regulation has long been an inspiration in the polymer chemistry field, aiming to combine sequence-controlled synthesis methods with the customizable and robust qualities of abiotic backbones. Sequence control is especially applicable to biomaterials, where tunable properties are necessary to match the dynamic criteria encountered in vivo. Implementing sequence control in synthetic platforms expands the range of properties available compared to purely biological backbones and affords adaptability through sequence, rather than compositional changes. Peptoids, or N-substituted glycines, are peptidomimetics with sidechains affixed to the amide backbone nitrogen, rather than the α-carbon. Peptoids can be synthesized with full sequence definition using the submonomer technique, which affords incorporation of any sidechain available as a primary amine. Thus, peptoids provide a versatile platform for advancing biomaterials, but their functional diversity necessitates thorough characterization of peptoid properties in relevance to sidechain chemistry and sequence effects. Here, we investigated sequence effects on the biodegradation of peptoid-peptide hybrids for potential use in synthetic biomaterials, namely by enzymatic and oxidative mechanisms. First, we examined the role of peptoid substitutions on the active site of matrix metalloproteinase (MMP)-degradable substrates by synthesizing a control peptide (VPLS↓LYSG, where ↓ indicates cleavage site) and a peptide-peptoid hybrid with a peptoid substitution at the P3 subsite (N-[2-(1-pyrrolidinyl)ethyl]glycine substituted for proline). We found that collagenase was able to hydrolyze this sequence completely at kinetic rates similar to the control substrate. Next, we examined the oxidative susceptibility of peptide-peptoid hybrids by synthesizing molecules composed of N-(2-methoxyethyl)glycine and proline residues in various sequence patterns. These substrates were incubated with hydrogen peroxide, and their degradation was monitored over time via liquid chromatography-mass spectrometry (LC-MS). We found that the peptoid backbone is susceptible to backbone oxidative degradation, similar to proline. Ongoing work will continue to expand the library of substrates under investigation to probe the design rules dictating enzyme-substrate selectivity and oxidative susceptibility. Ultimately, these results indicate that sequence-defined N-substitutions can be used to engineer substrates with tunable degradative properties for implementation in stimuli-responsive biomaterials. Comprehensive investigation of their degradative properties could allow for programmable degradation profiles and selective substrates amenable to both enzymatic and oxidative response mechanisms.