Question

Erythritol is a natural sugar abundant in fruits and fermenting foods. Pathogenic bacterial strains that catabolize erythritol contain four closely spaced genes, all involved in erythritol metabolism. One of the four genes (eryD) encodes a product that represses the expression of the other three genes. Erythritol catabolism is stimulated by erythritol. Present a regulatory model to account for the regulation of erythritol catabolism in such bacterial strains. Does this system appear to be under inducible or repressible control?

Short answer

Short Answer: The regulatory model for erythritol catabolism in pathogenic bacteria involves four genes. In the absence of erythritol, the product of eryD acts as a repressor, preventing the expression of the other three genes. When erythritol is present, it binds to the eryD product, causing a conformational change that allows the expression of the other genes and inducible control of the catabolic pathway.

Step-by-step solution

Identifying the key components of the regulatory model

Begin by identifying the different elements involved in the regulation of erythritol catabolism - the four genes, the product of eryD, erythritol, and any other relevant factors.

Creating a regulatory model for erythritol catabolism

Propose a model that accounts for the observed regulation based on the information provided. In the absence of erythritol, the product of eryD acts as a repressor and binds to the promoter region of the other three genes, preventing their expression (thus the catabolic pathway is "off"). When erythritol is abundant, it binds to the eryD product, causing a conformational change that releases the eryD product from the promoter region of the other genes. This allows the expression of the other three erythritol catabolic genes, and the catabolic pathway is "on".

Determine if the system is under inducible or repressible control

Whether a system is inducible or repressible depends on the default state of the pathway (is it initially "on" or "off"). In this case, the presence of erythritol activates the catabolic pathway of erythritol. Therefore, this regulation can be considered an inducible control system.

Key concepts

Inducible Control System

An inducible control system is a form of gene regulation where the expression of specific genes is controlled by the presence or absence of a certain molecule, often referred to as an inducer. In the context of erythritol catabolism, erythritol serves as this inducer. In an inducible system, the default state is "off," meaning that without the inducer, the genes involved in the specific metabolic pathway are not expressed.

Here, when erythritol is absent, the erythritol catabolic genes are prevented from being expressed by a repressor protein that binds to their promoter region. This system is advantageous for bacteria because it prevents unnecessary production of enzymes when the substrate (in this case, erythritol) is not present. When erythritol becomes available, it binds to the repressor, altering its shape so that it can no longer bind to the DNA. As a result, the genes are free to be transcribed, and the pathway is turned "on," allowing the bacteria to utilize erythritol.

This mechanism characterizes inducible systems, which are quite common in bacterial gene regulation, allowing efficient and responsive adaptation to environmental changes.

Erythritol Catabolism

Erythritol catabolism refers to the process through which bacterial cells break down erythritol, a type of sugar, to harness energy or for other cellular functions. For bacteria capable of utilizing erythritol, this metabolic pathway is crucial for survival, especially in environments rich in this sugar.

Bacterial strains that metabolize erythritol achieve this through a coordinated expression of several genes involved in processing the sugar. These genes are typically organized in clusters, facilitating their co-expression when necessary. In the presence of erythritol, these genes are activated, allowing the bacteria to produce the necessary enzymes that degrade erythritol into simpler compounds which can then enter various metabolic pathways.

This efficient system ensures that bacteria only expend energy to produce enzymes involved in erythritol breakdown when the sugar is available, optimizing energy utilization and resource allocation.

Repressor Proteins

Repressor proteins play a crucial role in gene regulation by preventing the transcription of target genes. They achieve this by binding to DNA sequences, often near the promoter region, to block the attachment of RNA polymerase. This prevents gene transcription and consequently halts protein production.

In the erythritol catabolism pathway, the product of the eryD gene functions as a repressor protein. In the absence of erythritol, this repressor binds to the promoter regions of the other genes involved in erythritol breakdown, keeping the pathway "off." By doing this, the cell conserves energy and resources by not producing unnecessary enzymes.

When erythritol is present, it interacts with the repressor protein, inducing a structural change that releases the repressor from the gene's promoter region. This release is crucial as it initiates the transcription of genes necessary for erythritol metabolism, showcasing how repressor proteins can switch metabolic pathways on or off in response to environmental cues.