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EF loop conformational change triggers ligand binding in beta-lactoglobulins.
Laura Ragona1, Federico Fogolari, Maddalena Catalano
1Laboratorio Risonanza Magnetica Nucleare, Istituto Macromolecole, Consiglio Nazionale delle Ricerche, via Bassini 15, 20133 Milano, Italy.
The Journal of Biological Chemistry
|July 15, 2003
Summary
Beta-lactoglobulins bind fatty acids through a pH-dependent EF loop opening mechanism. This conformational change, triggered by Glu89 protonation, is crucial for ligand binding in these lipocalin proteins.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Science
Background:
- Beta-lactoglobulins, lipocalin proteins, transport hydrophobic ligands like fatty acids.
- The precise mechanism of ligand binding and functional roles remain incompletely understood, with conflicting literature findings.
Purpose of the Study:
- To elucidate the mechanism of beta-lactoglobulin ligand binding.
- To comparatively analyze the binding properties of beta-lactoglobulins using integrated computational and experimental approaches.
Main Methods:
- Sequence-derived information analysis
- Structure-based electrostatic calculations
- Molecular docking simulations
- Nuclear Magnetic Resonance (NMR) experiments
- Theoretical pKa calculations
Main Results:
- The ligand binding mechanism is determined by the opening-closing of the EF loop, triggered by Glu89 protonation.
- Porcine beta-lactoglobulin exhibits an alkaline shift in Glu89 pKa (9.7 vs. 5.5 in bovine), enabling fatty acid binding at pH > 8.6.
- Key residues influencing electrostatic interactions and conformational changes were identified across various beta-lactoglobulins.
Conclusions:
- The EF loop conformational change is a common feature across all beta-lactoglobulins, essential for ligand binding.
- The high pH binding of porcine beta-lactoglobulin is potentially linked to lipase activity.
- This study provides a unified mechanism for beta-lactoglobulin ligand binding.