TY - JOUR
T1 - Effects of Calcium Binding on the Internal Dynamic Properties of Bovine Brain Calmodulin, Studied by NMR and Optical Spectroscopy
AU - Török, K.
AU - Lane, A. N.
AU - Martin, S. R.
AU - Janot, J. M.
AU - Bayley, P. M.
PY - 1992
Y1 - 1992
N2 - The dynamic properties of bovine brain calmodulin have been studied as a function of binding calcium ions, using a number of complementary spectroscopic methods. Rotational correlation times for proton-proton vectors within tyrosine and phenylalanine residues of calmodulin have been determined from time-dependent NOE measurements. In the presence of Ca2+, a range of rotational correlation times is observed. The longest value is consistent with Ca4-calmodulin having a markedly nonspherical shape in solution. In the absence of Ca2+, the rotational correlation times of all vectors are significantly shorter, indicating that several phenylalanine side chains in apocalmodulin have increased internal dynamics. Time-resolved tyrosine fluorescence anisotropy shows global correlation times broadly in agreement with the NMR results, but with an additional faster correlation time [≈600 ps]. Tyrosine residues in apocalmodulin have substantial segmental motion, which becomes significantly reduced, but not eliminated, when Ca2+ is bound. The correlation time for global rotation of Ca4-calmodulin increases from pH 7 to 4.5, indicating increased overall molecular asymmetry. This occurs without a significant change in total α-helix content as measured by circular dichroism. These results are consistent with the central region of Ca4-calmodulin being relatively flexible in solution at pH 7, but with the molecule adopting a more extended shape under more acidic conditions. The Ca2+-induced change in α-helix content can be mimicked by protonation. The α-helix content of Ca4-calmodulin in solution appears less than in the crystal structure; additional a-helix is induced in partially nonaqueous solutions, particularly at acidic pH, as used in crystallization conditions.
AB - The dynamic properties of bovine brain calmodulin have been studied as a function of binding calcium ions, using a number of complementary spectroscopic methods. Rotational correlation times for proton-proton vectors within tyrosine and phenylalanine residues of calmodulin have been determined from time-dependent NOE measurements. In the presence of Ca2+, a range of rotational correlation times is observed. The longest value is consistent with Ca4-calmodulin having a markedly nonspherical shape in solution. In the absence of Ca2+, the rotational correlation times of all vectors are significantly shorter, indicating that several phenylalanine side chains in apocalmodulin have increased internal dynamics. Time-resolved tyrosine fluorescence anisotropy shows global correlation times broadly in agreement with the NMR results, but with an additional faster correlation time [≈600 ps]. Tyrosine residues in apocalmodulin have substantial segmental motion, which becomes significantly reduced, but not eliminated, when Ca2+ is bound. The correlation time for global rotation of Ca4-calmodulin increases from pH 7 to 4.5, indicating increased overall molecular asymmetry. This occurs without a significant change in total α-helix content as measured by circular dichroism. These results are consistent with the central region of Ca4-calmodulin being relatively flexible in solution at pH 7, but with the molecule adopting a more extended shape under more acidic conditions. The Ca2+-induced change in α-helix content can be mimicked by protonation. The α-helix content of Ca4-calmodulin in solution appears less than in the crystal structure; additional a-helix is induced in partially nonaqueous solutions, particularly at acidic pH, as used in crystallization conditions.
UR - http://www.scopus.com/inward/record.url?scp=0026536393&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0026536393&partnerID=8YFLogxK
U2 - 10.1021/bi00128a020
DO - 10.1021/bi00128a020
M3 - Article
C2 - 1554727
AN - SCOPUS:0026536393
SN - 0006-2960
VL - 31
SP - 3452
EP - 3462
JO - Biochemistry
JF - Biochemistry
IS - 13
ER -