Creating a TALE protein with unbiased 5'-T binding

Area of Science:

• Molecular Biology
• Genetics
• Biotechnology

Background:

• Transcription activator-like effectors (TALEs) are valuable tools for targeted genome engineering.
• A significant limitation of TALEs is their requirement for a 5' terminal T nucleotide (5'-T) in their binding sites.
• This 5'-T constraint restricts the precise targeting of specific DNA sequences.

Purpose of the Study:

• To overcome the 5'-T constraint associated with TALE DNA binding.
• To develop TALE variants capable of targeting DNA sequences irrespective of the 5' terminal nucleotide.
• To enhance the versatility of TALEs for genome engineering applications.

Main Methods:

• Site-directed mutagenesis was employed to substitute tryptophan 232 in the dHax3 N-terminal repeat-1 loop.
• A library of repeat-1 mutants was generated through randomization of four amino acid residues in the hairpin loop region.
• Directed evolution techniques were applied to the randomized library to select for TALE variants with altered 5'-base specificity.

Main Results:

• Point mutation at tryptophan 232 was insufficient to eliminate the 5'-T binding requirement.
• Directed evolution successfully yielded repeat-1 mutants that could target DNA sequences without a 5'-T requirement.
• The repeat-1 loop region of dHax3 was identified as crucial for accommodating the 5'-base.

Conclusions:

• The repeat-1 loop region is critical for TALE DNA binding specificity.
• Molecular evolution of the TALE repeat-1 region is an effective strategy to remove the 5'-T constraint.
• This advancement significantly expands the utility of TALEs for targeting any DNA sequence in genome engineering.