Analysis of Ca²⁺/Mg²⁺ Selectivity in α-lactalbumin and Ca²⁺-binding Lysozyme Reveals a Distinct Mg²⁺-specific Site in Lysozyme

Authors

Sergei E. Permyakov, Institute for Biological Instrumentation of the Russian Academy of Sciences
Tatyana I. Khokhlova, Institute for Biological Instrumentation of the Russian Academy of Sciences
Vladimir N. Uversky, University of South FloridaFollow
Eugene A. Permyakov, Institute for Biological Instrumentation of the Russian Academy of Sciences

Document Type

Article

Publication Date

2010

Keywords

A-lactalbumin, Lysozyme, Thermo-dynamics, Phase Transition, Phase Diagram, Statediagram, Thermal Stability, Ligand Binding, Metalbinding, Metal Selectivity

Digital Object Identifier (DOI)

https://doi.org/10.1002/prot.22776

Abstract

The triggering of Ca²⁺ signaling pathways relies on Ca²⁺/Mg²⁺ specificity of proteins mediating these pathways. Two homologous milk Ca²⁺-binding proteins, bovine α-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 Ca²⁺/Mg²⁺ by native proteins is entropy-driven. Both proteins exhibit strong temperature dependences of apparent affinities to Ca²⁺ and Mg²⁺, due to low thermal stabilities of their apo-forms and relatively high unfavorable enthalpies of Mg²⁺ association. The ratios of their apparent affinities to Ca²⁺ and Mg²⁺, 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 Ca²⁺ and Mg²⁺ binding with experimental data strongly suggests that the association of Ca²⁺ and Mg²⁺ ions with bLA is a competitive process, whereas the primary Mg²⁺ site of EQL is different from its Ca²⁺-binding site. The later conclusion is corroborated by qualitatively different molar ellipticity changes in near-UV region accompanying Mg²⁺ and Ca²⁺ association. The Ca²⁺/Mg²⁺ selectivity of Mg²⁺-site of EQL is below an order of magnitude. EQL exhibits a distinct Mg²⁺-specific site, probably arising as an adaptation to the extracellular environment. Proteins 2010. © 2010 Wiley-Liss, Inc.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Proteins: Structure, Function, and Bioinformatics, v. 78, issue 12, p. 2571-2723

Scholar Commons Citation

Permyakov, Sergei E.; Khokhlova, Tatyana I.; Uversky, Vladimir N.; and Permyakov, Eugene A., "Analysis of Ca²⁺/Mg²⁺ Selectivity in α-lactalbumin and Ca²⁺-binding Lysozyme Reveals a Distinct Mg²⁺-specific Site in Lysozyme" (2010). Molecular Medicine Faculty Publications. 468.
https://digitalcommons.usf.edu/mme_facpub/468