Ligand binding calcium

Forty-four amino acid module characterized by three internal disulfide bridges and an octahedrical cage for a calcium ion. Complement-type repeats are found in many cell surface proteins and form the ligand-binding domain of receptors of the LDL receptor gene family. 

For example, Barlow and Margoliash [33] showed that phosphate, chloride, iodide, and sulfate, in decreasing order of effect, reduced the electrophoretic mobihty of human cytochrome c at pH 6.0 by up to a factor of 2. The cations lithium, sodium, potassium, and calcium had no effect. It is possible to account for the binding equilibria of these counterions so that the titration and electrophoresis results can be compared however, in many of the early electrophoresis experiments these data were not available and relevant conditions were not recorded or controlled. For general discussions on the extensive field of ligand binding to proteins, see Cantor and Schimmel [60] and van Holde [403]. 

Haiech, J. Klee, C.B. Demaille, J.G. Haiech, J. Effects of cations on affinity of calmodulin for calcium ordered binding of calcium ions allows the specific activation of calmodulin-stimulated enzymes. Theoretical approach to study of multiple ligand binding to a macromolecule. Biochemistry 1981, 20, 3890-3897. 

Calcineurin is part of a signaling pathway that is activated by a rise in intracellular calcium upon ligand binding to a cell membrane receptor. The rise in Ca activates calcineurin s phosphatase activity, which dephosphorylates cytoplasmic NF-AT transcription factor family members. Dephosphorylated NF-AT-members enter the nucleus and bind to DNA in cooperation with other transcription factors, e.g. AP-1. By this way many target genes in diverse tissues can be activated. 

This increase is thought to be one of the early steps involved in so-called signal transduction and can result in the activation of enzyme systems responsible for subsequent metabolic or developmental changes. Lymphocytes show increases in intracellular calcium in response to many kinds of specific and nonspecific surface ligand binding, some of which lead to the cellular changes that we associate with an immune response. Many other classes of cells also show calcium changes in response to stimulation. 

Quirk PL, et al. Three putative N-glycosylation sites within the murine 5-HT3A receptor sequence affect plasma membrane targeting, ligand binding, and calcium influx in heterologous mammalian cells. J Neurosci Res 2004 77(4) 498-506. 

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