TY - JOUR
T1 - Structural basis for the evolutionary inactivation of Ca2+ binding to synaptotagmin 4
AU - Dai, Han
AU - Shin, Ok Ho
AU - Machius, Mischa
AU - Tomchick, Diana R.
AU - Südhof, Thomas C.
AU - Rizo, Josep
N1 - Funding Information:
We thank A. Joachimiak and the staff of the Structural Biology Center beamlines 19BM and 19ID at the Advanced Photon Source for assistance in X-ray data collection. Use of the Argonne National Laboratory Structural Biology Center beamlines at the Advanced Photon Source was supported by the US Department of Energy, Office of Biological and Environmental Research, under contract no. W-31-109-ENG-38. This work was supported by US National Institutes of Health grant NS-40944 to J.R.
PY - 2004/9
Y1 - 2004/9
N2 - The neuronal protein synaptotagmin 1 functions as a Ca2+ sensor in exocytosis via two Ca2+ -binding C2 domains. The very similar synaptotagmin 4, which includes all the predicted Ca2+- binding residues in the C2B domain but not in the C2A domain, is also thought to function as a neuronal Ca2+ sensor. Here we show that, unexpectedly, both C2 domains of fly synaptotagmin 4 exhibit Ca2+-dependent phospholipid binding, whereas neither C 2 domain of rat synaptotagmin 4 binds Ca2+ or phospholipids efficiently. Crystallography reveals that changes in the orientations of critical Ca2+ ligands, and perhaps their flexibility, render the rat synaptotagmin 4 C2B domain unable to form full Ca2+-binding sites. These results indicate that synaptotagmin 4 is a Ca2+ sensor in the fly but not in the rat, that the C 2+-binding properties of C2 domains cannot be reliab y predicted from sequence analyses, and that proteins clearly identified as orthologs may nevertheless have markedly different functional properties.
AB - The neuronal protein synaptotagmin 1 functions as a Ca2+ sensor in exocytosis via two Ca2+ -binding C2 domains. The very similar synaptotagmin 4, which includes all the predicted Ca2+- binding residues in the C2B domain but not in the C2A domain, is also thought to function as a neuronal Ca2+ sensor. Here we show that, unexpectedly, both C2 domains of fly synaptotagmin 4 exhibit Ca2+-dependent phospholipid binding, whereas neither C 2 domain of rat synaptotagmin 4 binds Ca2+ or phospholipids efficiently. Crystallography reveals that changes in the orientations of critical Ca2+ ligands, and perhaps their flexibility, render the rat synaptotagmin 4 C2B domain unable to form full Ca2+-binding sites. These results indicate that synaptotagmin 4 is a Ca2+ sensor in the fly but not in the rat, that the C 2+-binding properties of C2 domains cannot be reliab y predicted from sequence analyses, and that proteins clearly identified as orthologs may nevertheless have markedly different functional properties.
UR - http://www.scopus.com/inward/record.url?scp=4344616380&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=4344616380&partnerID=8YFLogxK
U2 - 10.1038/nsmb817
DO - 10.1038/nsmb817
M3 - Article
C2 - 15311271
AN - SCOPUS:4344616380
SN - 1545-9993
VL - 11
SP - 844
EP - 849
JO - Nature Structural and Molecular Biology
JF - Nature Structural and Molecular Biology
IS - 9
ER -