2. Site-selected incorporation of 5-carboxymethylaminomethyl(-2-thio)uridine into RNA sequences by phosphoramidite chemistry
Grazyna Leszczynska, Jakub Pięta, Karolina Wozniak, Andrzej Malkiewicz Org Biomol Chem. 2014 Feb 21;12(7):1052-6. doi: 10.1039/c3ob42302f.
5-Carboxymethylaminomethyluridine (cmnm(5)U) and 5-carboxymethylaminomethyl-2-thiouridine (cmnm(5)s(2)U) are located at the wobble position in several cytosolic and mitochondrial tRNA sequences. In this paper, we report the first site-selected incorporation of cmnm(5)U and cmnm(5)s(2)U into RNA sequences by phosphoramidite chemistry on a CPG solid support. Trifluoroacetyl and 2-(trimethylsilyl)ethyl were selected for the protection of the amine and carboxyl functions, respectively.
3. 19F NMR of trifluoroacetyl-labeled cysteine mutants of myoglobin: structural probes of nitric oxide bound to the H93G cavity mutant
M R Thomas, S G Boxer Biochemistry. 2001 Jul 24;40(29):8588-96. doi: 10.1021/bi0101087.
Nitric oxide (NO) binds to the myoglobin (Mb) cavity mutant, H93G, forming either a 5- or 6-coordinate Fe--NO heme complex. The H93G mutation replaces the proximal histidine of Mb with glycine, allowing exogenous ligands to occupy the proximal binding site. In the absence of the covalently attached proximal ligand, NO could bind to H93G from the proximal side of the heme rather than the typical diatomic binding pocket on the distal side when the 5-coordinate complex forms. The question of whether NO binds on the distal or proximal side was addressed by (19)F NMR. Site-directed mutagenesis was used to introduce unique cysteine residues at the protein surface on either the distal (S58C) or proximal (L149C) side, approximately equidistant from and perpendicular to the heme plane of both wild-type and H93G Mb. The cysteine thiols were alkylated with 3-bromo-1,1,1-trifluoroacetone to attach a trifluoroacetyl group at the mutation site. (19)F NMR spectra of 5-coordinate, NO bound S58C/H93G and L149C/H93G double mutants depict peaks with line widths of 100 and 23 Hz, respectively. As fluorine peaks broaden with increasing proximity to paramagnetic centers, such as 5-coordinate Fe--NO, the (19)F NMR data are consistent with NO binding in the distal heme pocket of H93G, even in the absence of a sixth axial ligand. Additionally, (19)F NMR spectra are reported for deoxy, oxy, CO, met CN, and met H(2)O forms of the labeled cysteine mutants. These results demonstrate that the fluorine probes are sensitive to subtle conformational changes in the protein structure due to ligation and oxidation state changes of the heme iron in Mb.