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Site-selective chemical pyrophosphorylation of proteins using tag-and-modify approach.

Periodic Reporting for period 1 - PyroPhosphoProtein (Site-selective chemical pyrophosphorylation of proteins using tag-and-modify approach.)

Reporting period: 2016-04-01 to 2018-03-31

Site-selective protein modification is a powerful chemical biology tool that allows protein labelling, tracking in cells, studying enzyme functions, or creating better therapeutics. Different methods were developed for construction of precisely modified proteins. One of the powerful strategies is a two-step “tag-and-modify” approach, which takes advantage of unique chemical properties of dehydroalanine (Dha). In the first step, Dha (“tag”) is introduced into the position of interest providing protein with a reactive handle that is further modified. The approach is particularly useful for installation of various post-translational modifications (PTM) and natural amino acid mimics since it leaves ‘zero scar’ in protein structure. This project further broadened the scope of “tag-and-modify” approach by developing methods for (a) direct protein pyrophosphorylation, (b) installing histidine isosteres into enzyme active sites using unprecedented aza Michael addition to Dha. Moreover, stereoselectivity of thia-Michael addition to Dha in protein was explored.
The results generated during the project have contributed to state-of-the-art by broadening a set of tools available for protein modification using unique chemical properties of Dha. The method for site-selective chemical pyrophosphorylation of full length protein giving ppCys (mimic of natural ppSer) and its non-hydrolysable analogue was developed. Next, an unprecedented strategy for post-translational creation of β,γ-C,N bonds in proteins using Dha chemistry (aza-Michael addition) was described. This approach was further used to introduce histidine regioisomers, Hiso and azaHiso, into enzyme active sites for precise probing contributing roles of histidine size and H-bonding toward enzyme activity. Finally, stereoselectivity of thia Michael addition to Dha in protein was investigated. The results of the project resulted in scientific publication in ACS Central Science journal (ACS Cent. Sci. 2017, 3, 1168), review on protein modification via dehydroalanine chemistry (Curr. Opin. Chem. Biol. 2018, in press) and were presented and discussed at international conferences.
Protein modification via Dha allows ‘zero scar’ protein mutagenesis that in turn allows creation of precise biomimics of natural amino acids and/or post-translational modifications. During the project, a review was published discussing approaches to modify proteins via dehydroalanine with emphasis on recent applications ranging from creating modified nucleosomes to modulating protein functions. This review is expected to be useful source of information for the chemical biology community.
Until now, many proteins have been found to be pyrophosphorylated in vitro but the real significance of protein pyrophosphorylation in vivo remains poorly understood due to lack of chemical biology tools to study this novel post-translational modification. Here we developed a novel method for preparation of pure, well defined pyrophosphorylated proteins and their stable analogs offering long awaited tool for probing of pyrophosphorylation function.
Previously, β,γ-C,S (thia-Michael addition); β,γ-C,Se (selena-Michael addition) and β,γ-C,C (radical addition) bonds were formed post-translationally through Dha modification in proteins. Here, β,γ-C,N (aza-Michael addition) was described providing a novel protein conjugation method as well as a general tool for installing histidine mimics into proteins. These mimics were shown to be useful in dissecting histidine contribution to enzyme activity.
The project complied with the basic principles of the European Research Area by fostering research training, collaboration, mobility and knowledge transfer. It has enabled scientific and personal development of individuals and further promoted Europe as centre of research excellence.