Difference between revisions of "Part:BBa K2110004"

Latest revision as of 17:21, 13 October 2016

D-alanyl-D-alanine dipeptidase gene

Peptidoglycan is the major constituent of cell wall of bacterial like E.coli. The D-alanyl-D-alanine dipeptidase gene (ddpX) exists in the genome of E.coli. The counterpart of ddpX, VanX, which has the same effect as ddpX, exists in many gram-positive bacterial like Enterococcus faecalis and Streptomyces toyocaensis because they need it to hydrolyze the D-Ala-D-Ala and transfer the D-Ala-D-Ala residue of peptidoglycan to D-Ala-D-Lac residue so that the antibiotic vancomycin cannot combine the peptidoglycan to cause the destruction of cell wall. However, in gram-negative bacterial like E.coli, which own the robust outer membrane that can resist the vancomycin, the hydrolase ddpX with the same effects also exists. This is strange because the gram-negative bacterial have no necessity to own this kind of seemly dangerous hydrolase. Actually the ddpX in E.coli has another vital use when they are under starvation conditions. The ddpX can hydrolyze the D-Ala-D-Ala in their cell wall to produce the D-Ala as the carbon source to maintain their life. This mechanism is only carried out when they are under starvation conditions. If the ddpX gene is overexpressed, the cell wall will be damaged and cell lysis will occur.

Sequence and Features

Results

We did a experiment to measure the cell lysis effect of ddpX gene. We simply use the IPTG inducible T7 promoter to regulate the expression of ddpX gene. The result is as follows.