Analysis of Ca2+/Mg2+ selectivity in alpha-lactalbumin and Ca(2+)-binding lysozyme reveals a distinct Mg(2+)-specific site in lysozyme.
Abstract: The triggering of Ca(2+) signaling pathways relies on Ca(2+)/Mg(2+) specificity of proteins mediating these pathways. Two homologous milk Ca(2+)-binding proteins, bovine alpha-lactalbumin (bLA) and equine lysozyme (EQL), were analyzed using the simplest "four-state" scheme of metal- and temperature-induced structural changes in a protein. The association of Ca(2+)/Mg(2+) by native proteins is entropy-driven. Both proteins exhibit strong temperature dependences of apparent affinities to Ca(2+) and Mg(2+), due to low thermal stabilities of their apo-forms and relatively high unfavorable enthalpies of Mg(2+) association. The ratios of their apparent affinities to Ca(2+) and Mg(2+), being unusually high at low temperatures (5.3-6.5 orders of magnitude), reach the values inherent to classical EF-hand motifs at physiological temperatures. The comparison of phase diagrams predicted within the model of competitive Ca(2+) and Mg(2+) binding with experimental data strongly suggests that the association of Ca(2+) and Mg(2+) ions with bLA is a competitive process, whereas the primary Mg(2+) site of EQL is different from its Ca(2+)-binding site. The later conclusion is corroborated by qualitatively different molar ellipticity changes in near-UV region accompanying Mg(2+) and Ca(2+) association. The Ca(2+)/Mg(2+) selectivity of Mg(2+)-site of EQL is below an order of magnitude. EQL exhibits a distinct Mg(2+)-specific site, probably arising as an adaptation to the extracellular environment.
Copyright 2010 Wiley-Liss, Inc.
Publication Date: 2010-07-06 PubMed ID: 20602456DOI: 10.1002/prot.22776Google Scholar: Lookup
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Summary
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The research article examines how two milk proteins – bovine alpha-lactalbumin and equine lysozyme – interact with calcium and magnesium ions, revealing a unique magnesium-binding site in the equine lysozyme protein that might be a result of adaptation to the extracellular environment.
Overview of the Research
- The research investigates how two proteins present in milk interact with calcium and magnesium ions. Both these proteins have been previously shown to have roles in calcium signaling pathways, which are important for many biological functions. These proteins are bovine alpha-lactalbumin (bLA) and equine lysozyme (EQL).
- The analysis employs a simple “four-state” scheme that represents different structural states of a protein, such as the free protein and the protein bound to either calcium or magnesium ions, affected by temperature.
Key Findings
- The study affirms that the binding of both calcium and magnesium ions to these proteins is entropy-driven, meaning it is driven by an increase in disorder. Both proteins show strong temperature dependencies in their affinities for calcium and magnesium, attributed to the low thermal stabilities of their unbound forms and unfavorable enthalpies of magnesium association.
- Interestingly, the affinity ratios of these proteins to calcium and magnesium are extremely high at lower temperatures but reach values typical of EF-hand motifs, a common calcium-binding protein structure, at physiological temperatures.
- The combination of the model and experimental findings suggest that the binding of calcium and magnesium to bLA is a competitive process, while EQL features a primary magnesium-binding site that is distinctly separate from its calcium-binding site.
- The study further backs up this conclusion with the evidence of significantly different changes in molar ellipticity in the near-UV region when magnesium and calcium ions bind to EQL. These changes suggest that different regions of the protein are affected by the binding of each ion.
- The researchers also determine that the calcium/magnesium selectivity of EQL’s magnesium site is relatively low, less than an order of magnitude. This finding, combined with other evidence, supports the idea that EQL has a unique magnesium-specific binding site, possibly due to adaptation to its extracellular environment.
Implications of the Study
- This study contributes to our understanding of how proteins mediate calcium signaling pathways, which are critical for cell function and signaling.
- The discovery of a distinct magnesium-binding site in EQL could provide new insights into protein evolution and adaptation. It could also open up new avenues for researching protein-ion interactions and their roles in biological functions.
Cite This Article
APA
Permyakov SE, Khokhlova TI, Uversky VN, Permyakov EA.
(2010).
Analysis of Ca2+/Mg2+ selectivity in alpha-lactalbumin and Ca(2+)-binding lysozyme reveals a distinct Mg(2+)-specific site in lysozyme.
Proteins, 78(12), 2609-2624.
https://doi.org/10.1002/prot.22776 Publication
Researcher Affiliations
- Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow region 142290, Russia.
MeSH Terms
- Animals
- Binding Sites
- Calcium / chemistry
- Cattle
- Horses
- Humans
- Ions / chemistry
- Lactalbumin / chemistry
- Lactalbumin / metabolism
- Magnesium / chemistry
- Muramidase / chemistry
- Muramidase / metabolism
- Protein Denaturation
- Temperature
- Thermodynamics
Citations
This article has been cited 4 times.- Legrand D, Herbaut M, Durin Z, Brysbaert G, Bardor M, Lensink MF, Foulquier F. New insights into the pathogenicity of TMEM165 variants using structural modeling based on AlphaFold 2 predictions.. Comput Struct Biotechnol J 2023;21:3424-3436.
- Permyakov EA. α-Lactalbumin, Amazing Calcium-Binding Protein.. Biomolecules 2020 Aug 20;10(9).
- Vallone R, La Verde V, D'Onofrio M, Giorgetti A, Dominici P, Astegno A. Metal binding affinity and structural properties of calmodulin-like protein 14 from Arabidopsis thaliana.. Protein Sci 2016 Aug;25(8):1461-71.
- Bruhn O, Grötzinger J, Cascorbi I, Jung S. Antimicrobial peptides and proteins of the horse--insights into a well-armed organism.. Vet Res 2011 Sep 2;42(1):98.
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