Ligand entry in human ileal bile acid-binding protein is mediated by histidine protonation

Gergő Horváth, O. Egyed, Changguo Tang, M. Kovács, András Micsonai, J. Kardos, Orsolya Toke

Research output: Contribution to journalArticle

Abstract

Human ileal bile acid-binding protein (hI-BABP) has a key role in the intracellular transport of bile salts. To explore the role of histidine protonation in the binding process, the pH-dependence of bile salt binding and internal dynamics in hI-BABP was investigated using NMR spectroscopy and biophysical tools. Thermodynamic and kinetic measurements show an increase in the overall binding affinity and the association rate constant of the first binding step below the pK a of the histidines, suggesting that ligand binding is favoured by the protonated state. The overlap between residues exhibiting a high sensitivity to pH in their backbone amide chemical shifts and protein regions undergoing a global ms conformational exchange indicate a connection between the two processes. According to 15 N NMR relaxation dispersion analysis, the slow motion is most pronounced at and above the pK a of the histidines. In agreement with the NMR measurements, MD simulations show a stabilization of the protein by histidine protonation. Hydrogen-bonding and van der Waals interactions mediating the flow of information between the C/D- and G/H-turn regions hosting the three histidines, suggest a complex way of pH-governed allosteric regulation of ligand entry involving a transition between a closed and a more open protein state.

Original languageEnglish
Article number4825
JournalScientific reports
Volume9
Issue number1
DOIs
Publication statusPublished - Dec 1 2019

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Histidine
Ligands
Bile Acids and Salts
Allosteric Regulation
Proteins
Hydrogen Bonding
Thermodynamics
Amides
Magnetic Resonance Spectroscopy
human AKR1C2 protein

ASJC Scopus subject areas

  • General

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Ligand entry in human ileal bile acid-binding protein is mediated by histidine protonation. / Horváth, Gergő; Egyed, O.; Tang, Changguo; Kovács, M.; Micsonai, András; Kardos, J.; Toke, Orsolya.

In: Scientific reports, Vol. 9, No. 1, 4825, 01.12.2019.

Research output: Contribution to journalArticle

Horváth, Gergő ; Egyed, O. ; Tang, Changguo ; Kovács, M. ; Micsonai, András ; Kardos, J. ; Toke, Orsolya. / Ligand entry in human ileal bile acid-binding protein is mediated by histidine protonation. In: Scientific reports. 2019 ; Vol. 9, No. 1.
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AU - Micsonai, András

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