Bacteria And Signal Perception And Transduction Mechanisms

Bacteria and signal perception and transduction mechanisms

Introduction

Cellular communication is important because specialized tissues are made up of cells and these allow to maintain harmonious and coordinated functioning through the various mechanisms.

On the other hand, prokaryotic organisms live in environments in which factors vary constantly, such as pH, temperature, nutrient concentration, bacteria, the same species and others, and therefore competition. Therefore, they have to adapt their metabolism to these changes to spend the minimum energy, being more efficient. For what they need some mechanism that allows them to perceive signals of the environment and communicate with each other, in order to make an adequate response to the changes to which they are continuously exposed.

Signal transduction mechanisms

Prokaryotes to adapt their metabolism to environmental changes, need a mechanism that allows them to perceive environmental signals and communicate with each other. For this they use a signal transduction mechanism in two components.

The two component system is a signal transduction system that uses phosphate groups to control gene transcription and protein activity. It has two components mainly: a sensor kinase protein that detects the signals of the external environment and a replacement regulatory protein that regulates the cell.

• Sensoring kinase protein: They are transmembrane proteins, they usually have an external perplapasmiso domain where they receive the signal, and an internal catoplasmic catalog.

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• Regulatory protein: cytoplasmic protein that receives the signal when phosphorylates. It is usually a DNA union protein, thus controlling gene transcription.

A balanced regulatory system must have a feedback loop that consists of a regulatory circuit with an initial signal stop so that the process does not start again and again. This is achieved with phosphatase, which is an enzyme that eliminates the phosphoryl group of the regulatory response protein at constant speed.

There are two component regulatory systems that regulate certain genes that are those that give rise to the replacement protein. However, two component systems seem to be less widely distributed among Archaea species and are practically absent in bacteria.

Two component regulatory systems

There are numerous two component systems;An interesting example is the OMPR response regulator. When OMPR this phosphorylated activates the transcription of the OMPC gene and represses the transcription of the OMPF gene. In this way, the osmolarity of the environment is controlled.

Another example is the Nose Regulatory System controls a set of genes that allow the use of nitrate and nitrite as alternative electron acceptors during aerobic respiration. The NAR system contains two different sensor kinases and two response regulators. In addition, all genes regulated by this system are also controlled by FNR Protein, a global regulator for genes involved in anaerobic respiration.

Below two very studied examples of these two component systems will be developed: the system that controls sporulation and chemotaxisis.

Sporulation

In sporulation control (Figure 1), the Kin A protein is the sensor kinase. It serves as a transmitter of the self-ophosphorylate signal in a histidine residue in response to environmental signals. The SPO0F protein acts as a receiver that transfers the Kin phosphoryl group to an aspartic acid residue on its surface;Spo0f then doa your phosphoryl group to a Spo0b histidine. Then participate in the SPO0A protein, which acts as a response regulatory. It has an aspartate domain that collects the spo0b phosphoryl group and becomes an active transcriptional regulator, controlling sporulation by two SIGMA factors. Then the polymerase rna transcribes sporulation genes.

Chemiotaxis

Chemiotaxism is a type of phenomenon in which bacteria and other cells of unicellular or multicellular organisms direct their movements according to the concentration of certain chemical substances in their environment. If these are interesting the bacteria will move towards the greatest concentration, if it is harmful they will move away from it. This movement consists in the control of the movement of the scourges. It can be positive or negative.

Chemiotaxis responds complex to attractants and repellent. Swimming regulation affects protein activity instead of their synthesis. The chemicals of the medium bind to membrane receptors called chemotactic proteins accepting methylos (MCPS). This methylation adaptation allows the system to return to its initial state due to the continued presence of a signal.

The answer is regulated by a complex system (Figure 2), in which the CHEA protein acts as a sensory kinase and the Chey protein as a response regulator. MCP receptors are immersed in the plasma membrane with exposed parts both in and out. The perplapsmic side of each MCP has a binding site for one or several attractive molecules, and can also have some site of repellent molecules. The cytoplasmic side interacts with two proteins. The Chew joins the MCP and helps to join Chea. When the MCP is not linked to an attractive, it stimulates Chea to self-deforilating with ATP. This autophosphorylation is inhibited when MCP joins an attractive. Then the chea can donate its phosphate group to Chey or Cheb. If Chey is phosphoryila, passes to its active conformational state and turns the scourge in the direction of the clock needles, while before it did the contrary;As a consequence the bacteria stuck a shake. The phosphate group is removed from Chey about 10 seconds later by the chez protein. This short period makes the bacteria very sensitive to changes in the concentration of attractive molecules. As long as there are no attractants, phosphorylation remains in Chea and the bacteria does not paste changes in its course and follows a straight line.

But this system also needs that it is also possible to keep in the attractive, not to continue moving. So an adaptation system is necessary that checks the presence of the attractive molecule and stops in it. This adaptation is made thanks to the methylation of MCP receptors. These receptors can be put by the action of the adenosyl Metionine (SAM). The reaction is catalyzed by Cher, constantly adding methyl groups to the MCP. When Chea’s phosphoryila, so does check, which when it is in phosphorylated state acts as desmeilase, eliminated the MCP methyl groups.

The degree of methylation affects the configuration of the MCP protein, therefore affecting its ability to join the attractive molecule. When they are very methylated, they release the attractive, being unable to join him. While when they are little methylated they can easily join the attractive. Through this methylation/dissectilation system, the degree of sensitivity to the attractive is controlled, which also allows constantly verifying the presence of attractants in the environment.

self-induction mechanisms

Bacteria are also able to communicate with each other. For this they use a different system, called self-induction mechanism. In these systems there is also a response regulatory protein that when activated regulates the transcription of the DNA;There are also signs that activate regulatory protein. A good example is the quorum sensing.

Quorum sensing

In the perception of the quorum sensing, the signal is called autoinductor, which is a small molecule that goes abroad by a diffusion mechanisms. They go abroad in favor of concentration gradient. If the exterior concentration is too high, the signal, which acts as a self-inductor, will begin to accumulate in the cytoplasm, until the concentration is high enough to interact with the regulatory protein. On the other hand, so that the autinductors accumulate abroad there must be many bacteria that are secreting;So its concentration is an indirect measure of the number of bacteria.

The perception of Quorum Sensing was first discovered as the mechanism to regulate the emission of light in bioluminescent bacteria in such a way that when the concentration of bacteria was large enough they produced light and otherwise they did not emit light.

The first system that was studied was in great negative bacteria (Figure 3);In them the most common signal are the lactonas acyl-homerine (HSLS), which are derived from fatty acids that are formed from Coa and Sam. These HSLS are spreading towards Diana cells, which when they reach a high enough level, joins a protein receiver and trigger a conformational change. Normally activates complex. This gene also produces HSL amplifying the signal and releasing more self-inductor.

A whole series of genes are controlled by a quorum perception system including some in pathogenic bacteria, such as pseudomonas. These present an interesting and important function, promoting the formation of biofilms. For example, Pseudomonas aeruginosa, bacteria that has a key role in cystic fibrosis. Biipels formation is an important factor for bacteria, since it protects it from antibiotics. In addition, thanks to the formation of biofilms, quorum detection will be more effective because there will be less dilution and HSL levels will increase rapidly. By forming the complex signal-regulator there is a certain transcription, which generates virulence factors. With an average density of bacteria, a chronic infection occurs, while with a high, even more virulence factors are expressed, giving rise to acute infection.

In large positive bacteria, the signals are peptides, which go outside and act from there, that is, without entering the cell, since, if they enter they could be quickly degraded by the peptidases of the cytosol. To capture the presence of these signals, a two component system is used. The Quorum mechanism also has a series of advantages:

• Allows bacteria to increase their survival. As for example in bioluminescence, that when it is produced in a group it is advantageous, while if it did a single bacterium it can be a disadvantage since it consumes a lot of energy.
• Virulence. It is more advantageous to produce virulence factors in a high number, since if there were few the host’s immune system could easily eliminate them.
• Antibiotic production. That serve to eliminate other bacteria that could compete with them.

conclusion

The prokaryotes are organisms that are very adapted to the places where they live, therefore, to respond to any temperature variation, pH, nutrient concentration, quantity of bacteria, etc., is essential for survival.

The mechanisms of perception and transduction of signals are ways that help prokaryotes to detect these changes in the environment, as well as the presence of other bacteria, responding to them properly, regulating the transcription of certain specific genes. Therefore, these systems have been fundamental in the survival and evolution of these organisms.

Bibliography

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