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Trends Biochem Sci. 2005 Sep;30(9):490-7.

Morpheeins--a new structural paradigm for allosteric regulation.

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  • BioMolecular Structure and Function Group, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA. Eileen.Jaffe@fccc.edu


Classic models for the allosteric regulation of protein function consider an equilibrium among protein structures of constant oligomeric multiplicity. The morpheein (mor-phee'-in) concept expands this model to include a dynamic equilibrium of protein structures wherein a protein monomer can exist in more than one conformation and each monomer conformation dictates a different quaternary structure of finite multiplicity and different functionality. The morpheein concept provides a new framework for understanding allosteric regulation, kinetic cooperativity and hysteresis. Porphobilinogen synthase constitutes a prototype morpheein ensemble comprising several interconverting quaternary structure isoforms; one monomer conformation dictates assembly of a high-activity octamer, whereas an alternative monomer conformation dictates assembly of a low-activity hexamer. It is proposed here that the behavior of some other allosteric enzymes reflect dynamic morpheein equilibrium systems and six candidate proteins are enumerated.

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