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Characterization of calretinin I–II as an EF‐hand, Ca 2+ , H + ‐sensing domain
Author(s) -
Palczewska Małgorzata,
Batta Gyula,
Groves Patrick,
Linse Sara,
Kuźnicki Jacek
Publication year - 2005
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.051369805
Subject(s) - chemistry , calcium , protonation , crystallography , nuclear magnetic resonance spectroscopy , calmodulin , fluorescence spectroscopy , calcium binding protein , elution , sepharose , inorganic chemistry , biophysics , fluorescence , analytical chemistry (journal) , stereochemistry , chromatography , biochemistry , organic chemistry , ion , physics , quantum mechanics , biology , enzyme
Calretinin, a neuronal protein with well‐defined calcium‐binding properties, has a poorly defined function. The pH dependent properties of calretinin (CR), the N‐terminal (CR I–II), and C‐terminal (CR III–VI) domains were investigated. A drop in pH within the intracellular range (from pH 7.5 to pH 6.5) leads to an increased hydrophobicity of calcium‐bound CR and its domains as reported by fluorescence spectroscopy with the hydrophobic probe 2‐(p‐toluidino)‐6‐naphthalenesulfonic acid (TNS). The TNS data for the N‐ and C‐terminal domains of CR are additive, providing further support for their independence within the full‐length protein. Our work concentrated on CR I–II, which was found to have hydrophobic properties similar to calmodulin at lower pH. The elution of CR I–II from a phenyl‐Sepharose column was consistent with the TNS data. The pH‐dependent structural changes were further localized to residues 13–28 and 44–51 using nuclear magnetic resonance spectroscopy chemical shift analysis, and there appear to be no large changes in secondary structure. Protonation of His 12 and/or His 27 side chains, coupled with calcium chelation, appears to lead to the organization of a hydrophobic pocket in the N‐terminal domain. CR may sense and respond to calcium, proton, and other signals, contributing to conflicting data on the proteins role as a calcium sensor or calcium buffer.