Site-directed mutagenesis identifies the positively charged residue lysine-46 essential for the function of the immunity protein PedB

Asparagine and Glutamine Residues Participate in Protein Covalent Binding by Epoxide Metabolite of 8-Epidiosbulbin E Acetate In Vitro and In Vivo

Dioscorea Bulbifera L. (DBL), an effective traditional Chinese medicine, has been restricted because of multiple reports that it can cause severe hepatotoxicity. 8-Epidiosbulbin E acetate (EEA), one of the main components of DBL, can induce severe liver injury. It has been reported that EEA can be metabolized by CYP3A to the corresponding cis-enedial intermediate which alkylates the lysine residues of proteins to form pyrroline derivatives. The present study unexpectedly found that the reactive intermediate reacted with the amide groups of asparagine (Asn) and glutamine (Gln) residues of hepatic proteins of mice treated with EEA. The amide-derived protein modification increased with the increase in the dose administered. Like the adduction of the primary amine of lysine residues, the electrophilic metabolite reacted with the amide groups of Asn and Gln residues to offer the corresponding pyrrolines. The structures of the pyrrolines were confirmed by mass spectrometry and nuclear magnetic resonance spectroscopy.

[A method for introducing mutations into large vectors]

BACKGROUND AND OBJECTIVE

In vitro site-directed mutagenesis is a routine technique in molecular biology labs. However, although there are numbers of related methods available, most of these methods are not suitable for introducing mutations into large vectors.

METHODS

In this report, we describe a method which is highly effective for this purpose. Our method is based on the other site-directed method we recently reported. The basic protocol of our method is as follows: (1) Synthesize a pair of vector primers based on the sequences around the region to be mutated, each containing a suitable type IIs endonuclease restriction site; meanwhile, synthesize a pair of short complementary oligonucleotides which forms a mutagenic fragment after annealing; (2) Synthesize a pair of bridge primers which can specifically bind to a site in the vector sequence, each containing a suitable type IIs endonuclease restriction site; (3) Perform PCR reactions using these Vector primers and Bridge primers; (4) Digest the PCR products with the corresponding type IIs restriction enzyme; (5) Ligate the digested fragment with the mutagenic fragment to make the desired mutant.

RESULTS

Using this protocol, we have introduced mutations into a vector larger than 9 kb. The results shows that the mutation rates are more that 90%.

CONCLUSIONS

Our method provides a useful tool for performing site-directed mutagenesis experiment in large vector.