Directed mutagenesis of large multi-subunit protein complexes by plasmid sub-fragmentation

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Site-directed mutagenesis is crucial for protein functional studies.
• Mutagenizing large protein complexes is challenging due to replication fidelity and amplification issues.

Purpose of the Study:

• To develop an efficient method for site-directed mutagenesis of large protein complexes.
• To overcome limitations in DNA replication and amplification for complex genetic engineering.

Main Methods:

• Developed a plasmid sub-fragmentation technique for DNA coding sequences.
• Dissected the 15.1 kb E. coli Complex I nuo genes into 900 bp fragments with overlapping regions.
• Utilized unique primer sequences for amplification by standard DNA polymerases.
• Employed Gibson assembly for efficient recombination of mutated fragments into expression vectors.

Main Results:

• Successfully created a plasmid library of shorter DNA sequences for accurate long-range elongation by DNA polymerase.
• Demonstrated high success rates in introducing point mutations into a large pBAD expression vector (21.3 kb) by sub-cloning E. coli Complex I into 20 fragments.
• Achieved efficient Gibson assembly of mutated fragments, enabling accurate mutagenesis.

Conclusions:

• Plasmid sub-fragmentation is an efficient method for mutagenesis of large, multi-subunit protein complexes.
• This technique advances mechanistic studies of large bioenergetics protein complexes, including respiratory Complex I.
• Facilitates functional studies of proteins with homologous subunits.