TY - JOUR
T1 - Detection of electrostatic molecular binding using the water proton signal
AU - Zhou, Yang
AU - Bie, Chongxue
AU - van Zijl, Peter C.M.
AU - Xu, Jiadi
AU - Zou, Chao
AU - Yadav, Nirbhay N.
N1 - Funding Information:
This research was supported by NIH grants EB015032, EB025295, and EB031771. Y.Z. receives support from National Natural Science Foundation of China (82171904), Key Laboratory for Magnetic Resonance and Multimodality Imaging of Guangdong Province (2020B1212060051) and SIAT Innovation Program for Excellent Young Researchers. C.B. thanks China Scholarship Council (201906970024) for financial support.
Publisher Copyright:
© 2022 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.
PY - 2022/8
Y1 - 2022/8
N2 - Purpose: Saturation transfer MRI has previously been used to probe molecular binding interactions with signal enhancement via the water signal. Here, we detail the relayed nuclear overhauser effect (rNOE) based mechanisms of this signal enhancement, develop a strategy of quantifying molecular binding affinity, i.e., the dissociation constant ((Formula presented.)), and apply the method to detect electrostatic binding of several charged small biomolecules. Another goal was to estimate the detection limit for transient receptor-substrate binding. Theory and Methods: The signal enhancement mechanism was quantitatively described by a three-step magnetization transfer model, and numerical simulations were performed to verify this theory. The binding equilibria of arginine, choline, and acetyl-choline to anionic resin were studied as a function of ligand concentration, pH, and salt content. Equilibrium dissociation constants ((Formula presented.)) were determined by fitting the multiple concentration data. Results: The numerical simulations indicate that the signal enhancement is sufficient to detect the molecular binding of sub-millimolar (∼100 μM) concentration ligands to low micromolar levels of molecular targets. The measured rNOE signals from arginine, choline, and acetyl-choline binding experiments show that several magnetization transfer pathways (intra-ligand rNOEs and intermolecular rNOEs) can contribute. The rNOEs that arise from molecular ionic binding were influenced by pH and salt concentration. The molecular binding strengths in terms of (Formula presented.) ranged from 70–160 mM for the three cations studied. Conclusion: The capability to use MRI to detect the transient binding of small substrates paves a pathway towards the detection of micromolar level receptor-substrate binding in vivo.
AB - Purpose: Saturation transfer MRI has previously been used to probe molecular binding interactions with signal enhancement via the water signal. Here, we detail the relayed nuclear overhauser effect (rNOE) based mechanisms of this signal enhancement, develop a strategy of quantifying molecular binding affinity, i.e., the dissociation constant ((Formula presented.)), and apply the method to detect electrostatic binding of several charged small biomolecules. Another goal was to estimate the detection limit for transient receptor-substrate binding. Theory and Methods: The signal enhancement mechanism was quantitatively described by a three-step magnetization transfer model, and numerical simulations were performed to verify this theory. The binding equilibria of arginine, choline, and acetyl-choline to anionic resin were studied as a function of ligand concentration, pH, and salt content. Equilibrium dissociation constants ((Formula presented.)) were determined by fitting the multiple concentration data. Results: The numerical simulations indicate that the signal enhancement is sufficient to detect the molecular binding of sub-millimolar (∼100 μM) concentration ligands to low micromolar levels of molecular targets. The measured rNOE signals from arginine, choline, and acetyl-choline binding experiments show that several magnetization transfer pathways (intra-ligand rNOEs and intermolecular rNOEs) can contribute. The rNOEs that arise from molecular ionic binding were influenced by pH and salt concentration. The molecular binding strengths in terms of (Formula presented.) ranged from 70–160 mM for the three cations studied. Conclusion: The capability to use MRI to detect the transient binding of small substrates paves a pathway towards the detection of micromolar level receptor-substrate binding in vivo.
KW - IMMOBILISE
KW - acetyl-choline
KW - arginine
KW - choline
KW - dissociation constant
KW - electrostatic interaction
KW - exchange relayed NOE
KW - molecular binding
KW - saturation transfer MRI
UR - http://www.scopus.com/inward/record.url?scp=85127372046&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85127372046&partnerID=8YFLogxK
U2 - 10.1002/mrm.29230
DO - 10.1002/mrm.29230
M3 - Article
C2 - 35394084
AN - SCOPUS:85127372046
SN - 0740-3194
VL - 88
SP - 901
EP - 915
JO - Magnetic resonance in medicine
JF - Magnetic resonance in medicine
IS - 2
ER -