The allosteric modulation of thyroxine-binding globulin affinity is entropy driven

ARIEL A. PETRUK; LABANDA, MARíA S; ALVAREZ, ROSA MARíA S.; MARCELO A. MARTí

BIOCHIMICA ET BIOPHYSICA ACTA-GENERAL SUBJECTS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 1830 p. 3570 - 3577

0304-4165

Background: Thyroxine-binding globulin (TBG) is a non-inhibitory member of the serpin family of proteins whose main structural element is the reactive center loop (RCL), that, upon cleavage by proteases, is inserted into the protein core adopting a â-strand conformation (stressed to relaxed transition, S-to-R). After S-to-R transition thyroxine (T4) affinity decreases. However, crystallographic studies in the presence or absence of the hormone in different states are unable to show significant differences in the structure and interactions of the binding site. Experimental results also suggest the existence of several S states (differing in the number of inserted RCL residues), associated with a differential affinity.Thyroxine-binding globulin (TBG) is a non-inhibitory member of the serpin family of proteins whose main structural element is the reactive center loop (RCL), that, upon cleavage by proteases, is inserted into the protein core adopting a â-strand conformation (stressed to relaxed transition, S-to-R). After S-to-R transition thyroxine (T4) affinity decreases. However, crystallographic studies in the presence or absence of the hormone in different states are unable to show significant differences in the structure and interactions of the binding site. Experimental results also suggest the existence of several S states (differing in the number of inserted RCL residues), associated with a differential affinity.â-strand conformation (stressed to relaxed transition, S-to-R). After S-to-R transition thyroxine (T4) affinity decreases. However, crystallographic studies in the presence or absence of the hormone in different states are unable to show significant differences in the structure and interactions of the binding site. Experimental results also suggest the existence of several S states (differing in the number of inserted RCL residues), associated with a differential affinity.finity decreases. However, crystallographic studies in the presence or absence of the hormone in different states are unable to show significant differences in the structure and interactions of the binding site. Experimental results also suggest the existence of several S states (differing in the number of inserted RCL residues), associated with a differential affinity.ficant differences in the structure and interactions of the binding site. Experimental results also suggest the existence of several S states (differing in the number of inserted RCL residues), associated with a differential affinity.finity. Methods: To shed light into the molecular basis that regulates T4 affinity according to the degree of RCL insertion in TBG,weperformed extendedmolecular dynamics simulations combinedwith several thermodynamic analysis of the T4 binding to TBG in three different S states, and in the R state.To shed light into the molecular basis that regulates T4 affinity according to the degree of RCL insertion in TBG,weperformed extendedmolecular dynamics simulations combinedwith several thermodynamic analysis of the T4 binding to TBG in three different S states, and in the R state. Results: Our results show that, despite T4 binding in the protein by similar interactions in all states, a good correlation between the degree of RCL insertion and the binding affinity, driven by a change in TBG conformational entropy, was observed.Our results show that, despite T4 binding in the protein by similar interactions in all states, a good correlation between the degree of RCL insertion and the binding affinity, driven by a change in TBG conformational entropy, was observed.finity, driven by a change in TBG conformational entropy, was observed. Conclusion: TBG allosteric regulation is entropy driven. The presence of multiple S states may allow more efficient T4 release due to protease activity.TBG allosteric regulation is entropy driven. The presence of multiple S states may allow more efficient T4 release due to protease activity.ficient T4 release due to protease activity. General significance: The presented results are clear examples of howcomputer simulationmethods can reveal the thermodynamic basis of allosteric effects, and provide a general framework for understanding serpin allosteric affinity regulation. © 2013 Elsevier B.V. All rights reservedficance: The presented results are clear examples of howcomputer simulationmethods can reveal the thermodynamic basis of allosteric effects, and provide a general framework for understanding serpin allosteric affinity regulation. © 2013 Elsevier B.V. All rights reservedfinity regulation. © 2013 Elsevier B.V. All rights reserved