Metal Binding

BpyAla is a metal-ion chelating amino acid. Researchers genetically encode proteins with metal-binding unnatural amino acid (UAA) for protein engineering and functional studies (Xie, Liu et al. 2007, Lee, Spraggon et al. 2009, Drienovská, Rioz-Martínez et al. 2015). BpyAla has been shown to strongly chelate transition metal ions including Fe2+, Fe3+, Cu2+, Ru2+, Ru3+, Co2+, and Co3+ (Xie, Liu et al. 2007). Additionally, BpyAla is able to form multimeric metal ion structures and can be used to synthetically direct conjugation and protein-protein interactions.

Site specific incorporation of BpyAla relies upon an orthogonal tRNA and amino acyl tRNA synthetase derived from a Methanococcus jannaschii amber suppressor tyrosyl-tRNA (MjtRNATyr CUA/tyrosyl-tRNA synthestase (MjTyrRS)(Xie, Liu et al. 2007). Previous studies have used 0.2 µM-1.0 µM of BpyAla in media with BL21(DE3) or DH10β cells for incorporation of BpyAla into proteins at an engineered TAG codon (Xie, Liu et al. 2007, Lee, Spraggon et al. 2009, Drienovská, Rioz-Martínez et al. 2015).

HQ-Ala is a metal-ion chelating amino acid forming stable complexes with transition metals and some lanthanides. Researchers genetically encode proteins with metal-binding unnatural amino acid (UAA) for protein engineering and functional studies (Lee, Spraggon et al. 2009, Wang, Parrish et al. 2009). HQ-Ala. Addition of Zn2+ creates a fluorescent probe with excitation and emission maxima of ~400 nm and ~545 nm, respectively (Wang, Parrish et al. 2009, Zhou and Hao 2015).

Site specific incorporation of HQ-Ala relies upon an orthogonal tRNA and amino acyl tRNA synthetase derived from a Methanococcus jannaschii amber suppressor tyrosyl-tRNA (MjtRNATyr CUA/tyrosyl-tRNA synthestase (MjTyrRS) (Lee, Spraggon et al. 2009). One study reported the production of 1.5 mg/L of full length protein in minimal media supplemented with 1 mM HQ-Ala (Lee, Spraggon et al. 2009). The fluorescence capabilities of HQ-Ala provide a unique utility in developing biological metal ion sensors.