Synthetic Thiol and Selenol Derived Amino Acids for Expanding the Scope of Chemical Protein Synthesis

Abstract

Cells employ post-translational modifications (PTMs) as key mechanisms to expand proteome diversity beyond the inherent limitations of a concise genome. The ability to incorporate post-translationally modified amino acids into protein targets via chemical ligation of peptide fragments has enabled the access to homogeneous proteins bearing discrete PTM patterns and empowered functional elucidation of individual modification sites. Native chemical ligation (NCL) represents a powerful and robust means for convergent assembly of two homogeneous, unprotected peptides bearing an N-terminal cysteine residue and a C-terminal thioester, respectively. The subsequent discovery that protein cysteine residues can be chemoselectively desulfurized to alanine has ignited tremendous interest in preparing unnatural thiol-derived variants of proteogenic amino acids for chemical protein synthesis following the ligation-desulfurization logic. Recently, the 21st amino acid selenocysteine, together with other selenyl derivatives of amino acids, have been shown to facilitate ultrafast ligation with peptidyl selenoesters, while the advancement in deselenization chemistry has provided reliable bio-orthogonality to PTMs and other amino acids. The combination of these ligation techniques and desulfurization/deselenization chemistries has led to streamlined synthesis of multiple structurally-complex, post-translationally modified proteins. In this review, we aim to summarize the latest chemical synthesis of thiolated and selenylated amino-acid building blocks and exemplify their important roles in conquering challenging protein targets with distinct PTM patterns.

N-Terminal Proline Editing for the Synthesis of Peptides with Mercaptoproline and Selenoproline: Mechanistic Insights Lead to Greater Efficiency in Proline Native Chemical Ligation

“…Native chemical ligation (NCL) and its variant expressed protein ligation (EPL) allow the synthesis of large, complex proteins with non-native and non-encodable functionalities that are incorporated via synthetically prepared segments. − NCL was originally described and is still most widely utilized via peptides and proteins with an N-terminal cysteine, which forms an amide bond upon reaction with peptides and proteins with C-terminal thioesters, via thioester exchange (transthioesterification) followed by S → N acyl transfer (Figure ). The scope of NCL with other N-terminal residues has been substantially expanded via the incorporation of thiols and selenols in other native amino acids (as amino acid surrogates), followed by desulfurization or deselenization. − …”

Harmony of Protein Tags and Chimeric Molecules Empowers Targeted Protein Ubiquitination and Beyond

“…Moreover, given that many proteins undergo various PTMs at different sites, achieving a homogeneous form of PTM becomes essential for unambiguous functional interpretation [ 30 , 31 ]. Such homogeneity can be achieved through in vitro chemical or semi-synthetic synthesis strategies but is a formidable challenge for in vivo studies [ 32 , 33 , 34 ].…”

Selenourea as a hydrogen bond donor catalyst and source of selenium for metal-, activator-free synthesis of selenoesters in a batch and flow reactor

“…20 Very limited literatures are reported which use selenoureas as organocatalysts, till date. Selenoesters are effective in in vivo model (amyloid β aggregation), 21 act as anticancer agents, 22 antimycobacterial agents, 23 facilitate reversal of cancer multi drug resistance, 24 act as precursors for Native chemical ligation (NCL), [25][26][27] diselenideselenoester ligation (DSL) 28,29 and synthesis of larger proteins, [30][31][32] and as synthon for synthesis of selenoacids 33a and acyl radicals. 33b…”