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Characterization of apo and partially saturated states of calerythrin, an EF‐hand protein from S. erythraea : A molten globule when deprived of Ca 2+
Author(s) -
Aitio Helena,
Laakso Tero,
Pihlajamaa Tero,
Torkkeli Mika,
Kilpeläinen Ilkka,
Drakenberg Torbjörn,
Serimaa Ritva,
Annila Arto
Publication year - 2001
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.31201
Subject(s) - molten globule , chemistry , protein secondary structure , crystallography , titration , amide , nmr spectra database , kinetics , small angle x ray scattering , calcium , dispersion (optics) , circular dichroism , spectral line , analytical chemistry (journal) , scattering , chromatography , biochemistry , organic chemistry , astronomy , optics , physics , quantum mechanics
Abstract Calerythrin, a four‐EF‐hand calcium‐binding protein from Saccharopolyspora erythraea , exists in an equilibrium between ordered and less ordered states with slow exchange kinetics when deprived of Ca 2+ and at low temperatures, as observed by NMR. As the temperature is raised, signal dispersion in NMR spectra reduces, and intensity of near‐UV CD bands decreases. Yet far‐UV CD spectra indicate only a small decrease in the amount of secondary structure, and SAXS data show that no significant change occurs in the overall size and shape of the protein. Thus, at elevated temperatures, the equilibrium is shifted toward a state with characteristics of a molten globule. The fully structured state is reached by Ca 2+ ‐titration. Calcium first binds cooperatively to the C‐terminal sites 3 and 4 and then to the N‐terminal site 1, which is paired with an atypical, nonbinding site 2. EF‐hand 2 still folds together with the C‐terminal half of the protein, as deduced from the order of appearance of backbone amide cross peaks in the NMR spectra of partially Ca 2+ ‐saturated states.