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Charge Distribution in 7-Methylguanine Regarding Cation- Interaction with Protein Factor eIF4E

Katarzyna Ruszczynska ^*, Krystyna Kamienska-Trela , Jacek Wojcik , Janusz Stepinski ^*, Edward Darzynkiewicz ^* and Ryszard Stolarski ^*

^* Department of Biophysics, Institute of Experimental Physics, Warsaw University, Warsaw, Poland; Institute of Organic Chemistry, Polish Academy of Sciences, Warsaw, Poland; and Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland

Correspondence: Address reprint requests to Ryszard Stolarski, Dept. of Biophysics, Institute of Experimental Physics, Warsaw University, 93 Zwirki & Wigury St. 02-089 Warszawa, Poland. Tel.: 48-22-554-0772; Fax: 48-22-554-0771; E-mail: stolarsk@biogeo.uw.edu.pl.

Electric charge distribution in mRNA 5' cap terminus has been exhaustively characterized in respect to the affinity for cap-binding proteins. Formation of the stacked configuration of positively charged 7-methylguanine in between two aromatic amino acid rings, known as sandwich cation- stacking, is thought to be prerequisite for the specific recognition of the cap by eukaryotic initiation factor eIF4E; i.e., discrimination between the cap and nucleotides without the methyl group at N(7). Nuclear magnetic resonance spectroscopy of ¹⁵N/¹³C-double-labeled 7-methylguanosine 5'-triphosphate and 7-methylguanosine, as well as their unsubstituted counterparts, GTP and guanosine, yielded characteristic changes of the electron-mediated spin-spin couplings and chemical shifts due to the methylation at N(7). The experimentally measured changes of the nuclear magnetic resonance parameters have been analyzed in respect to the electric charge distribution calculated by means of quantum chemical methods, and interpreted in terms of new proposed positive charge localization in the 7-methylguanine five-member ring.