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Capture and release of peptides is often a critical operation in the pathway to discovering materials with novel functions. However, the best methods for efficient capture impede facile release. To overcome this challenge, we report linkers based on secondary amino alcohols for the release of peptides after capture. These amino alcohols are based on serine (seramox) or isoserine (isoseramox) and can be incorporated into peptides during solid-phase peptide synthesis through reductive amination. Both linkers are quantitatively cleaved within minutes under NaIO4 treatment. Cleavage of isoseramox produced a native peptide N-terminus. This linker also showed broad substrate compatibility; incorporation into a synthetic peptide library resulted in the identification of all sequences by nanoLC-MS/MS. The linkers are cell compatible; a cell-penetrating peptide that contained this linker was efficiently captured and identified after uptake into cells. These findings suggest that such secondary amino alcohol based linkers might be suitable tools for peptide-discovery platforms., National Institutes of Health (Grants R01 GM110535, F32 GM133073), National Science Foundation (Grants 4000057398, 4000057441)

The billion tons of synthetic-polymer-based materials (i.e. plastics) produced yearly are a great challenge for humanity. Nature produces even more natural polymers, yet they are sustainable. Proteins are sequence-defined natural polymers that are constantly recycled when living systems feed. Digestion is the protein depolymerization into amino acids (the monomers) followed by their re-assembly into new proteins of arbitrarily different sequence and function. This breaks a common recycling paradigm where a material is recycled into itself. Organisms feed off of random protein mixtures that are "recycled" into new proteins whose identity depends on the cell's specific needs. In this study, mixtures of several peptides and/or proteins are depolymerized into their amino acid constituents, and these amino acids are used to synthesize new fluorescent, and bioactive proteins extracellularly by using an amino-acid-free, cell-free transcription-translation (TX-TL) system. Specifically, three peptides (magainin II, glucagon, and somatostatin 28) are digested using thermolysin first and then using leucine aminopeptidase. The amino acids so produced are added to a commercial TX-TL system to produce fluorescent proteins. Furthermore, proteins with high relevance in materials engineering (beta-lactoglobulin films, used for water filtration, or silk fibroin solutions) are successfully recycled into biotechnologically relevant proteins (fluorescent proteins, catechol 2,3-dioxygenase)., Advanced Materials, 33 (44), ISSN:0935-9648, ISSN:1521-4095

The billion tons of synthetic polymer-based materials (i.e. plastics) produced every year are one of the greatest challenges that humanity has to face. Nature produces even more natural polymers, yet they are sustainable. For example, proteins are sequence-defined natural polymers, that are constantly recycled when living systems feed. Indeed, digestion is the protein depolymerization into amino acids (i.e. the monomers) followed by their re-assembly into new proteins of arbitrarily different sequence and function. This process breaks a common recycling paradigm where a material is recycled into itself. Organisms feed of random protein mixtures that are ‘recycled’ into new proteins whose identity depends on the cell’s needs at the time of protein synthesis. Currently, advanced materials are increasingly made of proteins, but the abovementioned ideal recyclability of such materials has yet to be recognized and established. In this study mixtures of several (up to >30) peptides and/or proteins were depolymerized into their amino acid constituents, and these amino acids were used to synthesize new fluorescent, and bio-active proteins extra-cellularly by using an amino acid-free cell-free transcription-translation system. Proteins with high relevance in materials engineering (β-lactoglobulin films, used for water filtration, or silk fibroin solutions) were successfully recycled into biotechnologically relevant proteins (green, and red fluorescent proteins, catechol 2,3-dioxygenase). The potential long-term impact of this approach to recycling lies in its compatibility with circular-economy models where raw materials remain in use as long as possible, thus reducing the burden on the planet.