Protonation states of important acidic residues in the central Ca²âº ion binding sites of the Ca²âº-ATPase: a molecular modeling study.
Biochemistry
; 50(51): 11109-20, 2011 Dec 27.
Article
em En
| MEDLINE
| ID: mdl-22082179
ABSTRACT
The P-type ATPases are responsible for the transport of cations across cell membranes. The sarco(endo)plasmic reticulum Ca²âº-ATPase (SERCA) transports two Ca²âº ions from the cytoplasm to the lumen of the sarco(endo)plasmic reticulum and countertransports two or three protons per catalytic cycle. Two binding sites for Ca²âº ions have been located via protein crystallography, including four acidic amino acid residues that are essential to the ion coordination. In this study, we present molecular dynamics (MD) simulations examining the protonation states of these amino acid residues in a Ca²âº-free conformation of SERCA. Such knowledge will be important for an improved understanding of atomistic details of the transport mechanism of protons and Ca²âº ions. Eight combinations of the protonation of four central acidic residues, Glu309, Glu771, Asp800, and Glu908, are tested from 10 ns MD simulations with respect to protein stability and ability to maintain a structure similar to the crystal structure. The trajectories for the most prospective combinations of protonation states were elongated to 50 ns and subjected to more detailed analysis, including prediction of pK(a) values of the four acidic residues over the trajectories. From the simulations we find that the combination leaving only Asp800 as charged is most likely. The results are compared to available experimental data and explain the observed destabilization upon full deprotonation, resulting in the entry of cytoplasmic K⺠ions into the Ca²âº binding sites during the simulation in which Ca²âº ions are absent. Furthermore, a hypothesis for the exchange of protons from the central binding cavity is proposed.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Modelos Moleculares
/
Cálcio
/
Aminoácidos Acídicos
/
ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático
Tipo de estudo:
Prognostic_studies
Limite:
Animals
Idioma:
En
Revista:
Biochemistry
Ano de publicação:
2011
Tipo de documento:
Article
País de afiliação:
Dinamarca