1. Differential glycosylation in mutant vitamin D-binding protein decimates the binding stability of vitamin D.
- Author
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Usama, Khan Z, Ali A, Shah M, and Imran M
- Subjects
- Glycosylation, Humans, Molecular Dynamics Simulation, Protein Stability, Protein Conformation, Models, Molecular, Thermodynamics, Polymorphism, Single Nucleotide, Binding Sites, Mutant Proteins chemistry, Mutant Proteins metabolism, Protein Isoforms chemistry, Protein Isoforms metabolism, Protein Isoforms genetics, Vitamin D-Binding Protein metabolism, Vitamin D-Binding Protein genetics, Vitamin D-Binding Protein chemistry, Protein Binding, Vitamin D metabolism, Vitamin D chemistry, Mutation
- Abstract
Vitamin D (VD) is produced by the skin upon exposure to sunlight or is obtained from dietary sources. Several risk factors are associated with VD deficiency including mutations and post-translational modifications in its transport protein known as vitamin D binding protein (VDBP) or GC-globulin. The two common single nucleotide polymorphisms rs7041 and rs4588 create three major isoforms of VDBP, including GC-1F also called wild type, GC1S, and GC-2. The 3D models for both GC-1F and GC-2 were constructed in their glycosylated states to decipher the effect of these mutations on the overall conformational changes and VD-binding affinity. The binding affinities were estimated using the Molecular Mechanics Poison-Boltzmann surface area (MM-PBSA) method and conformational changes were investigated after free energy landscapes estimations. Total free energies suggest that GC-1F exhibits stronger affinity (ΔE = -116.09 kJ/mol) than GC-2 (ΔE = -95 kJ/mol) variant with VD. The GC-1F isoforms had more streamlined motion compared to GC-2 isoforms, predicting a trade-off between cross-talk residues that significantly impacts protein structural stability. The data suggest that glycation at Thr418 plays a vital role in the overall VDBP-VD affinity by stabilizing the N-T loop that holds the domain I (VD-pocket) and domain III intact. The loss of glycation in GC-2 has a pivotal role in the inter-domain conformational stability of VDBP, which may ultimately affect VD transportation and maturation. These findings describe a novel mechanism in how mutations distant from the VD-active site change the overall conformational of the VDBP and abrogate the VDBP-VD interaction.Communicated by Ramaswamy H. Sarma.
- Published
- 2024
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