Morpheein

Morpheein

Illustration of the morpheein model using dice to represent different conformations.

The term morpheein refers to a specific model of allosteric regulation in proteins, where the protein can exist in multiple distinct conformational states, each of which can assemble into different oligomeric forms. This model is distinct from the classical models of allostery, such as the Monod-Wyman-Changeux (MWC) model and the Koshland-Némethy-Filmer (KNF) model, in that it involves changes in the oligomeric state of the protein as part of the regulatory mechanism.

Overview

The morpheein model was proposed to explain certain observations in protein behavior that could not be adequately described by existing models of allostery. In this model, a protein can exist in different conformational states, termed "morpheein forms," which can assemble into different oligomeric structures. These different oligomeric forms can have distinct functional properties, allowing the protein to respond to various regulatory signals.

Mechanism

In the morpheein model, the protein undergoes a conformational change that alters its oligomeric state. This change can be triggered by the binding of a ligand, a change in environmental conditions, or other factors. The different oligomeric forms can have different affinities for substrates or inhibitors, different catalytic activities, or other functional differences.

The key features of the morpheein model include:

1. Conformational Diversity: The protein can adopt multiple conformations, each capable of forming distinct oligomers. 2. Oligomeric Assembly: The different conformations can assemble into oligomers with different stoichiometries and symmetries. 3. Functional Diversity: The different oligomeric forms have distinct functional properties, allowing for complex regulatory behavior.

Examples

Several proteins have been proposed to follow the morpheein model of regulation. One well-studied example is porphobilinogen synthase (PBGS), an enzyme involved in the biosynthesis of heme. PBGS can exist in different oligomeric forms, each with different catalytic properties, and its activity is regulated by the interconversion between these forms.

Significance

The morpheein model provides a framework for understanding complex regulatory mechanisms in proteins that cannot be explained by traditional models of allostery. It highlights the importance of conformational and oligomeric diversity in protein function and regulation.

Also see

• Allosteric regulation
• Protein conformation
• Oligomerization
• Porphobilinogen synthase

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