Part:BBa_K4169015

produce TMADH

After expressing, it'll produce trimethylamine dehydrogenase (TMADH (EC 1.5.99.7)). The enzyme TMADH is an iron–sulfur flavoprotein which catalyses the oxidative demethylation of trimethylamine (TMA) to dimethylamine and formaldehyde:
(CH₃)₃N + H₂O → (CH₃)₂NH + CH₂O +2H⁺ + 2e^- [1].

Metabolic Pathway

This enzyme is a complex iron-sulfur flavoprotein that transfers electrons to the soluble flavoprotein known as electron transferring flavoprotein [2]. It couldn't work extracellular isolated.

Figure 1.Pathways for trimethylamine metabolism in bacteria.

Protein Molecular Structures

Trimethylamine dehydrogenase (TMADH) exist as dimers.

Figure 2.Protein molecular structures of trimethylamine dehydrogenase.

At the same time, we found that the existing structural research on TMADH is relatively thorough through literature review. In combination with the results of mathematical modeling in the optimization of enzyme kinetics, we finally selected the V344C mutant and compared it with the unmutated TMADH to quantitatively detect the enzyme activity.

Engineering Success

We have taken a series verified experiment. From this dufficult gene can be expressed successfully and can be expressed an active protein successfully then.Although it was some basic molecular cloning research in the early stage, we still made a lot of efforts under the premise of many failures, and finally expressed active TMADH

The expression at the nucleic acid level

Plasmid(4μg) was synthesized by Genscript. Firstly, we centrifuged tmd plasmid powder at 5000rpm for 1 min, then added 40μg sterile ddH2O to dissolve it. The plasmid concentration was 100ng/μL. After diluting plasmid solution into10ng/μL, we transformed plasmids into competent cells E. coli BL21. The outcomes of colony PCR is showed below.

Figure 1. Colony PCR of E. coli BL21containing tmd plasmids.

The expression at the protein level

We performed SDS-PAGE to identify that trimethylamine dehydrogenase can be expressed. Because trimethylamine dehydrogenase (TMADHexist as dimers, the protein molecular weight would double. So, protein molecular weight of TMADH is 164.9kDa.

Figure 3. Control is E. coli BL21 without tmd. tmd is induced E. coli BL21 with tmd.

Detection of protein activity

We cultivated E. coli BL21 containing tmd, V344C tmd and E. coli BL21 without tmd (Blank) for about 3 hours (OD600 0.6~0.8). Then they were induced by 4mM theophylline for 9 hours. After adjusting the density of three tubes of bacteria and making them almost have no difference, we added some TMA into bacteria cultures to make the concentration of substrate TMA 5×10-5mol/L and continued to cultivate them. Take samples before we add TMA, and add TMA for 0 min, 10 min, 20min, 3h, 6h, 9h.

Figure 4. Concentration Changes of Metabolism Substrate DMA

Results show that expressed TMADH could metabolize TMA into DMA successfully. Also it can be seen that the mutant has higher activity than normal one, which is in line with the theoretical knowledge.But there are also something strange needs us to explore. More details can been seen in parts experience page.

Sequence and Features

Sequence and Features

Assembly Compatibility:

• 10
  INCOMPATIBLE WITH RFC[10]

  Illegal EcoRI site found at 388
  Illegal PstI site found at 183
  Illegal PstI site found at 1782
  
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal EcoRI site found at 388
  Illegal PstI site found at 183
  Illegal PstI site found at 1782
  
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal EcoRI site found at 388
  Illegal XhoI site found at 1717
  
• 23
  INCOMPATIBLE WITH RFC[23]

  Illegal EcoRI site found at 388
  Illegal PstI site found at 183
  Illegal PstI site found at 1782
  
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal EcoRI site found at 388
  Illegal PstI site found at 183
  Illegal PstI site found at 1782
  Illegal AgeI site found at 879
  
• 1000
  COMPATIBLE WITH RFC[1000]