Expanding the methionine toolkit: L-cyanohomoalanine as a multifunctional analog

Area of Science:

• Biochemistry
• Chemical Biology
• Molecular Biology

Background:

• Non-canonical amino acids (ncAAs) are essential tools for labeling and tracking biomolecules.
• Recombinant incorporation of ncAAs using native bacterial machinery simplifies protein labeling.
• Methionine analogs are particularly useful for probing protein synthesis and function.

Purpose of the Study:

• To investigate the incorporation of L-cyanohomoalanine (Cha), a methionine analog, into proteins using native E. coli machinery.
• To compare the efficiency and effects of Cha incorporation with L-methionine (Met) and L-azidohomoalanine (Aha).
• To assess the impact of Cha and Aha incorporation on protein stability and potential applications.

Main Methods:

• Expression of mutant superfolder GFP (sfGFP) in methionine auxotroph E. coli cultures supplemented with Cha, Met, or Aha.
• Growth rate analysis of E. coli in the presence of high concentrations of Aha and Cha.
• Mass spectrometry to confirm incorporation sites and N-terminal cleavage.
• Thermal melt analysis to evaluate protein stability after ncAAs incorporation.

Main Results:

• L-cyanohomoalanine (Cha) was successfully incorporated into sfGFP by E. coli methionyl-tRNA synthetase.
• Cha is non-toxic to E. coli, unlike L-azidohomoalanine (Aha) at high concentrations.
• Protein incorporation efficiency was lower for Cha compared to Met and Aha.
• Incorporation of Cha and Aha did not significantly affect sfGFP stability.
• N-terminal cleavage of incorporated amino acids was confirmed by mass spectrometry.

Conclusions:

• L-cyanohomoalanine (Cha) is a viable, non-toxic alternative for protein labeling via native E. coli machinery.
• Cha exhibits lower incorporation efficiency than Met or Aha, suggesting potential limitations for certain applications.
• The nitrile group of Cha offers unique reaction possibilities orthogonal to click chemistry and potential for vibrational spectroscopy.