Download MendeleyInaugural Article: Structural role of countertransport revealed in Ca2+ pump crystal structure in the absence of Ca2+.
Obara, K., Miyashita, N., Xu, C., Toyoshima, I., Sugita, Y., Inesi, G., Toyoshima, C.(2005) Proc Natl Acad Sci U S A 102: 14489-14496
- PubMed: 16150713
- DOI: https://doi.org/10.1073/pnas.0506222102
- Primary Citation of Related Structures:
2AGV - PubMed Abstract:
Ca(2+)-ATPase of sarcoplasmic reticulum is an ATP-powered Ca(2+) pump but also a H(+) pump in the opposite direction with no demonstrated functional role. Here, we report a 2.4-A-resolution crystal structure of the Ca(2+)-ATPase in the absence of Ca(2+) stabilized by two inhibitors, dibutyldihydroxybenzene, which bridges two transmembrane helices, and thapsigargin, also bound in the membrane region. Now visualized are water and several phospholipid molecules, one of which occupies a cleft between two transmembrane helices. Atomic models of the Ca(2+) binding sites with explicit hydrogens derived by continuum electrostatic calculations show how water and protons fill the space and compensate charge imbalance created by Ca(2+)-release. They suggest that H(+) countertransport is a consequence of a requirement for maintaining structural integrity of the empty Ca(2+)-binding sites. For this reason, cation countertransport is probably mandatory for all P-type ATPases and possibly accompanies transport of water as well.
Organizational Affiliation:
Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
