TY - JOUR
T1 - A 1.3-Å Structure of Zinc-bound N-terminal Domain of Calmodulin Elucidates Potential Early Ion-binding Step
AU - Warren, Julia T.
AU - Guo, Qing
AU - Tang, Wei Jen
N1 - Funding Information:
We would like to thank the staff at the Advanced Photon Source, Argonne National Laboratories, for their expert advice and assistance in our data collection. Special thanks to Zenon Grabarek and Raymond Hulse for their critical reading of our manuscript and helpful comments. This work was supported by Grant GM62548 from the National Institutes of Health and a Howard Hughes Medical Institute Undergraduate Research Fellowship. Use of the Argonne National Laboratory Structural Biology Center and BioCARS beam lines at the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Energy Research, under Contract W-31-109-ENG-38.
PY - 2007/11/23
Y1 - 2007/11/23
N2 - Calmodulin (CaM) is a 16.8-kDa calcium-binding protein involved in calcium-signal transduction. It is the canonical member of the EF-hand family of proteins, which are characterized by a helix-loop-helix calcium-binding motif. CaM is composed of N- and C-terminal globular domains (N-CaM and C-CaM), and within each domain there are two EF-hand motifs. Upon binding calcium, CaM undergoes a significant, global conformational change involving reorientation of the four helix bundles in each of its two domains. This conformational change upon ion binding is a key component of the signal transduction and regulatory roles of CaM, yet the precise nature of this transition is still unclear. Here, we present a 1.3-Å structure of zinc-bound N-terminal calmodulin (N-CaM) solved by single-wavelength anomalous diffraction phasing of a selenomethionyl N-CaM. Our zinc-bound N-CaM structure differs from previously reported CaM structures and resembles calcium-free apo-calmodulin (apo-CaM), despite the zinc binding to both EF-hand motifs. Structural comparison with calcium-free apo-CaM, calcium-loaded CaM, and a cross-linked calcium-loaded CaM suggests that our zinc-bound N-CaM reveals an intermediate step in the initiation of metal ion binding at the first EF-hand motif. Our data also suggest that metal ion coordination by two key residues in the first metal-binding site represents an initial step in the conformational transition induced by metal binding. This is followed by reordering of the N-terminal region of the helix exiting from this first binding loop. This conformational switch should be incorporated into models of either stepwise conformational transition or flexible, dynamic energetic state sampling-based transition.
AB - Calmodulin (CaM) is a 16.8-kDa calcium-binding protein involved in calcium-signal transduction. It is the canonical member of the EF-hand family of proteins, which are characterized by a helix-loop-helix calcium-binding motif. CaM is composed of N- and C-terminal globular domains (N-CaM and C-CaM), and within each domain there are two EF-hand motifs. Upon binding calcium, CaM undergoes a significant, global conformational change involving reorientation of the four helix bundles in each of its two domains. This conformational change upon ion binding is a key component of the signal transduction and regulatory roles of CaM, yet the precise nature of this transition is still unclear. Here, we present a 1.3-Å structure of zinc-bound N-terminal calmodulin (N-CaM) solved by single-wavelength anomalous diffraction phasing of a selenomethionyl N-CaM. Our zinc-bound N-CaM structure differs from previously reported CaM structures and resembles calcium-free apo-calmodulin (apo-CaM), despite the zinc binding to both EF-hand motifs. Structural comparison with calcium-free apo-CaM, calcium-loaded CaM, and a cross-linked calcium-loaded CaM suggests that our zinc-bound N-CaM reveals an intermediate step in the initiation of metal ion binding at the first EF-hand motif. Our data also suggest that metal ion coordination by two key residues in the first metal-binding site represents an initial step in the conformational transition induced by metal binding. This is followed by reordering of the N-terminal region of the helix exiting from this first binding loop. This conformational switch should be incorporated into models of either stepwise conformational transition or flexible, dynamic energetic state sampling-based transition.
KW - EF-hand motif
KW - X-ray crystallography
KW - calmodulin
KW - metal ion binding
KW - metal ion induced conformational switch
UR - http://www.scopus.com/inward/record.url?scp=35548964668&partnerID=8YFLogxK
U2 - 10.1016/j.jmb.2007.09.048
DO - 10.1016/j.jmb.2007.09.048
M3 - Article
C2 - 17942116
AN - SCOPUS:35548964668
SN - 0022-2836
VL - 374
SP - 517
EP - 527
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 2
ER -