Chemical Evolution of a Bacterial Proteome

We have changed the amino acid set of the genetic code of Escherichia coli by evolving cultures capable of growing on the synthetic noncanonical amino acid L ‐β‐(thieno[3,2‐b]pyrrolyl)alanine ([3,2]Tpa) as a sole surrogate for the canonical amino acid L ‐tryptophan (Trp). A long‐term cultivation experiment in defined synthetic media resulted in the evolution of cells capable of surviving Trp→[3,2]Tpa substitutions in their proteomes in response to the 20 899 TGG codons of the E. coli W3110 genome. These evolved bacteria with new‐to‐nature amino acid composition showed robust growth in the complete absence of Trp. Our experimental results illustrate an approach for the evolution of synthetic cells with alternative biochemical building blocks.     

Covalent Attachment of Cyclic TAT Peptides to GFP Results in Protein Delivery into Live Cells with Immediate Bioavailability

The delivery of free molecules into the cytoplasm and nucleus by using arginine‐rich cell‐penetrating peptides (CPPs) has been limited to small cargoes, while large cargoes such as proteins are taken up and trapped in endocytic vesicles. Based on recent work, in which we showed that the transduction efficiency of arginine‐rich CPPs can be greatly enhanced by cyclization, the aim was to use cyclic CPPs to transport full‐length proteins, in this study green fluorescent protein (GFP), into the cytosol of living cells. Cyclic and linear CPP–GFP conjugates were obtained by using azido‐functionalized CPPs and an alkyne‐functionalized GFP. Our findings reveal that the cyclic‐CPP–GFP conjugates are internalized into live cells with immediate bioavailability in the cytosol and the nucleus, whereas linear CPP analogues do not confer GFP transduction. This technology expands the application of cyclic CPPs to the efficient transport of functional full‐length proteins into live cells.     

In vivo incorporation of multiple noncanonical amino acids into proteins

Expansion of the standard genetic code enables the design of recombinant proteins with novel and unusual properties. Traditionally, such proteins have contained only a single type of noncanonical amino acid (NCAA) in their amino acid sequence. However, recently reported initial efforts demonstrate that it is possible with suppression-based methods to translate two chemically distinct NCAAs into a single recombinant protein by combining the suppression of different termination codons and nontriplet coding units (such as quadruplets). The possibility of expanding the code with various NCAAs simultaneously further increases the toolkit for the generation of multifunctionalized proteins.     

Genetically encoded photocrosslinkers as molecular probes to study G-protein-coupled receptors (GPCRs)

The genetic code was expanded with orthogonal pairs to introduce photoactivatable amino acids into G-protein-coupled receptors (GPCRs) in a noninvasive manner. In this way the receptor surface could be mapped by searching for specific ligand interaction sites and the complex dynamics could be studied. This method is also useful for probing the structure of GPCR complexes in living cells.     

Organic fluorine as a polypeptide building element: in vivo expression of fluorinated peptides, proteins and proteomes

Traditionally, the biological fluorination of complex biological systems like proteins is achieved through substitution of canonical amino acids or addition of fluorinated amino acids in the context of the standard genetic code. Ribosomal translation of monofluorinated amino acids into proteins often yields structures with minimal local changes in the interior but, on the same time, results in large global effects on characteristic features of the biopolymers (such as dramatically changed activity profile or folding stability). This is due to the novel and unique local interactions delivered by fluorine atoms such as (i) increase in the covalent radii (ii) changed polarities; (iii) changed hydrogen bond acceptor ability; (iv) altered water solubility as well as water ? organic solvent energy transfer. On the other hand, the biological incorporation of tri- or global fluorinated amino acids (such as trifluoroleucine, triflurovaline, and their hexafluoro counterparts, fluoromethionine and trifluoronorleucine etc.) represents still a challenge, as the natural structural scaffolds are optimized for hydrocarbon during evolution but not for fluorocarbon cores. Future work will be focused on the re-design of existing or de novo design of novel protein scaffolds capable of accommodating such building blocks into functional biologically active proteins and proteomes in the context of the viable cells.