The key difference between concerted and sequential model of allosterism is that in concerted mode, enzyme subunits are connected in such a way that a conformational change in one subunit is necessarily conferred to all other subunits, whereas in sequential model, subunits are not connected in such a way that a conformational change in one subunit induces a similar change in the others.
The concerted model and sequential model of allosterism can be described as two principal models of behavior of allosteric enzymes. These models were introduced in 1965 and 1966, respectively. Currently, we use both these models as a basis for interpreting experimental results. The concerted model has the advantage of being comparatively simple and describes the behavior of some enzyme systems very well. The sequential model, on the other hand, shows a certain amount of simplicity, but only for some realistic pictures of structures and behavior of proteins. This mode also deals with the behavior of some enzyme systems very well.
CONTENTS
1. Overview and Key Difference
2. What is the Concerted Model of Allosterism
3. What is the Sequential Model of Allosterism
4. Concerted vs Sequential Model of Allosterism in Tabular Form
5. Summary – Concerted vs Sequential Model of Allosterism
What is the Concerted Model of Allosterism?
The concerted model of allosterism postulates that enzyme subunits are connected in a way in which a conformational change in one subunit is necessarily conferred to all other subunits. This is also known as the symmetry model or MWC model. According to this model, all subunits must exist in the same conformation.
Figure 01: Allosteric Regulation (A – Active Site B – Allosteric Site C – Substrate D – Inhibitor E – Enzyme)
This model was introduced by Jacques Monod, Jeffries Wyman, and Jean-Pierre in 1965. According to this model, a protein has two conformations: active conformation R and inactive conformation T. R conformation binds the substrate tightly, whereas, in T conformation, the substrate is bonded less tightly.
One distinguishing feature of the concerted model is that the conformation of all subunits changes simultaneously. For example, in a hypothetical protein having two subunits, both subunits can change the conformation from the inactive T conformation to the active R conformation.
What is the Sequential Model of Allosterism?
The sequential model of allosterism can be described as a direct sequential model of allosteric behavior. This model has the distinguishing feature of binding the substrate that induces the conformational change from the T form to the R form. This led to the formation of the cooperative binding expression of this model.
Figure 02: Sequential Model
Moreover, in this model, all the activators and inhibitors are bound by the induced-fit mechanism. Here, the conformational change in the inhibitor or activator in one of the subunits affects the conformations of other subunits.
The most important features of the sequential model include: its subunits do not need to exist in the same conformation, its conformational changes are not conferred to all subunits, and molecules of substrates bind via the induced-fit protocol.
What is the Difference Between Concerted and Sequential Model of Allosterism?
The key difference between concerted and sequential model of allosterism is that in the concerted mode, a conformational change in one subunit is necessarily transmitted to all other subunits, whereas in the sequential model, a conformational change in one subunit does not induce a similar change in the others.
Summary – Concerted vs Sequential Model of Allosterism
The concerted model of allosterism is a model that postulates that enzyme subunits are connected in a way in which a conformational change in one subunit is necessarily conferred to all other subunits. The sequential model of allosterism is a direct sequential model of allosteric behavior. In this model, a conformational change in one subunit does not induce a similar change in the others. So, this is the key difference between concerted and sequential model of allosterism.
Reference:
1. “3.6: Allosteric Interactions.” Chemistry LibreTexts, Libretexts, 17 July 2020.
Image Courtesy:
1. “Allosteric Regulation” By Isaac Webb – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “KNF model” By Henry Jakubowski – Bio Libretexts (CC BY-SA 3.0) via Commons Wikimedia
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