Difference between revisions of "Part:BBa K1806001"

Latest revision as of 17:13, 21 September 2015

Helicobacter pylori catalase

This part is the coding sequence for the Helicobacter pylori catalase, which effectively catalyses the breakdown of hydrogen peroxide. The breakdown of hydrogen peroxide, which is an exothermic process, will be utilized to provide heat to the medium to increase temperature to counteract a shift that decreases the temperature of the host environment.

Catalase (also named as peroxidase) is the enzyme responsible for the breakdown of hydrogen peroxide, which is commonly found in nearly all living organisms that interact with oxygen.[1] The reaction catalyzed by catalase is as follows:

2H2O2 2H2O + O2 + heat [2]

This decomposition reaction produces significant levels of heat during the breakdown.[3] Also, the importance of this reaction is that it occurs in all oxidative organisms, making catalase an abundant enzyme and readily present in many targeted organisms.[4]

The aforementioned features of catalase make it suited for the needs of our project as an effective enzyme to stimulate an enzymatic heating process. The reason behind the selection of catalase as the enzyme for such the exothermic process was the inspiration drawn from the bombardier beetle.

The Bombardier Beetle and Catalase

The Bombardier Beetle (Brachinini) is a group of species that utilizes a explosive-induced spray pulsation system as a defense mechanism. As a response to external threat, the bombardier beetle sprays a chemically active liquid vapor from its abdomen. This vapor shows its function through the flammatory reaction of hydrogen peroxide.[5]

The dorsal structure of the bombardier beetle's abdomen allows several chambers to be found in its response system.[6] The reaction that our project focuses on occurs in the reaction chamber which is directly connected to the exit channel. In this channel, peroxidases which catalase the enzymatic reaction enter the liquid vapor.

The liquid that travels to the reaction chamber contains hydroquinine and high levels of hydrogen peroxide. The peroxidases that join the vapor in the reaction chamber prior to the pulsation initiate a flammatory reaction that continues after the pulsation and on the target. The bombardment of the bombardier beetle is hence a result of the mechanical excretion of a liquid vapor of catalase and hydrogen peroxide.[7] This method of flammation will also be utilized for our project.

Structure and Regulatory Mechanism

The catalase coding sequences that are adapted to our project were taken from two different organisms. One is the common HPI Catalase of E. coli controlled by the katG enzyme site. The second catalase to be used in the project is the HPC Catalase of H. pylori controlled by the katA enzyme site.

HPI catalase is expressed in E. coli as a result of oxidative stress. The tetramic catalase of E. coli, as previously mentioned, is controlled by the katG enzyme site. This enzyme site is regulated by the OxyR protein, a member of the LysR family of autoregulatory transcriptional activators. OxyR is naturally inactive in regulation, but is activated under oxidative stress stimulated by hydrogen peroxide. It has also been observed that OxyR increases the transcription of the katG enzyme site by 100-fold. The oxyR has a self-regulatory effect on its auto-synthesis, through end-product inhibition, meaning that the only factor that can stimulate an increase in oxyR concentration would be an increase in oxidative stress. Therefore, the synthesis of HPI catalase in E. coli is regulated by katG and oxyR.[8]

The highly catalase reliant H. pylori has a similar catalase function to that of E. coli. The enzyme site responsible for the control of catalase translation in H. pylori is the katA enzyme site. Just like katG, katA is stimulated by oxidative stress through autoregulatory transcriptional activators.[9] Fur and PerR are the factors maintaining transcriptional regulation in H. pylori.[10] The catalase translation and activity levels in H. pylori are significantly higher in respect to E. coli.[11] Both HPI and HPC catalase contain a heme group in their structure; however H. pylori has only one wild-type catalase, whereas E. coli has another catalase, which is HPII (produced only in anaerobic contiditions). Despite the structural differences in between H. pylori catalase and HPI catalase, both have the same regulatory mechanism.[12] This gives them the applicability in similar conditions.

Energetics of Catalase

HPC and HPI catalase can both function as a catalase and a peroxidase. The factors that affect the peroxidase functionality, however, are not in correlation with the factors that affect catalase activity, thus the hydrogen peroxide degradation. The hydrogen peroxide degradation is usually at maximum levels for the enzymatic activity. The entalphy values for these enzymatic are as follows:

Wild-type katG Coded HPI Catalase Entalphy: +17 kJ mol-1 [13]

Wild-type katA Coded HPC Catalase Entalphy: +100.4 kJ mol-1 [14]

These values show that both reactions have very high exothermic values per each mole. The H. pylori strains, however, are significantly higher, showing the efficiency of the reaction mechanism of HPC catalase. H. pylori produces catalase to maintain its life functions and it would be understandable that its catalase would be functioning at such levels of efficiency.

Cloning

The part was ligated to the pSB1C3 cloning vector and the transformation was verified with Colony PCR. Afterwards, the isolates cut with EcoR1 and Pst1 were cutchecked. The functionality of the cloning of these parts can be seen in the gel images taken and placed below. The images on the right show the expected bands in the gel run.

Sequence and Features

References

1 Langston, Matthew. SPECTROSCOPIC INVESTIGATION OF HELICOBACTER PYLORI CATALASE COMPOUND II. Pennsylvania: Master of Science, 2012. 1-83.