Ca^<2+> Release to Lumen from ADP-sensitive Phosphoenzyme E1PCa_2 without Bound K^+ of Sarcoplasmic Reticulum Ca^<2+>-ATPase
著者
山崎, 和生
(Yamasaki, Kazuo)
Daiho, Takashi
Danko, Stefania
Suzuki, Hiroshi
上位タイトル
Journal of Biological Chemistry
Vol.285,
No.49
(2010.
12)
,p.38674-
38683
識別番号
ISSN
0021-9258
DOI
10.1074/jbc.M110.183343
抄録
During Ca^<2+> transport by sarcoplasmic reticulum Ca^<2+>-ATPase, the conformation change of ADP-sensitive phosphoenzyme (E1PCa_2) to ADP-insensitive phosphoenzyme (E2PCa_2) is followed by rapid Ca^<2+> release into the lumen. Here, we find that in the absence of K^+, Ca^<2+> release occurs considerably faster than E1PCa_2 to E2PCa_2 conformation change. Therefore, the lumenal Ca^<2+> release pathway is open to some extent in the K^+-free E1PCa_2 structure. The Ca^<2+> affinity of this E1P is as high as that of the unphosphorylated ATPase (E1), indicating the Ca^<2+> binding sites are not disrupted. Thus, bound K^+ stabilizes the E1PCa_2 structure with occluded Ca^<2+>, keeping the Ca^<2+> pathway to the lumen closed. We found previously (Yamasaki, K., Wang, G., Daiho, T., Danko, S., and Suzuki, H. (2008) J. Biol. Chem. 283, 29144-29155) that the K^+ bound in E2P reduces the Ca^<2+> affinity essential for achieving the high physiological Ca^<2+> gradient and to fully open the lumenal Ca^<2+> gate for rapid Ca^<2+> release (E2PCa_2 → E2P + 2Ca^<2+>). These findings show that bound K^+ is critical for stabilizing both E1PCa_2 and E2P structures, thereby contributing to the structural changes that efficiently couple phosphoenzyme processing and Ca^<2+> handling.
