TY - JOUR
T1 - The transmembrane domain 6 of vacuolar H+-pyrophosphatase mediates protein targeting and proton transport
AU - Pan, Yih Jiuan
AU - Lee, Chien Hsien
AU - Hsu, Shen Hsing
AU - Huang, Yun Tzu
AU - Lee, Ching Hung
AU - Liu, Tseng Huang
AU - Chen, Yen Wei
AU - Lin, Shih Ming
AU - Pan, Rong Long
N1 - Funding Information:
We thank Mr. Hui-Hao Lin for his technical assistance on confocal microscopy. This work was supported by grants from National Science Council , Taiwan to R.L. Pan ( NSC 97-2311-B-007-003MY3 and NSC 97-2627-M-007-003 ) and CGMH-NTHU Joint Research No. 96N2421E1 to R.L. Pan.
PY - 2011/1
Y1 - 2011/1
N2 - Vacuolar H+-pyrophosphatase (V-PPase; EC 3.6.1.1) plays a significant role in the maintenance of the pH in cytoplasm and vacuoles via proton translocation from the cytosol to the vacuolar lumen at the expense of PPi hydrolysis. The topology of V-PPase as predicted by TopPred II suggests that the catalytic site is putatively located in loop e and exposed to the cytosol. The adjacent transmembrane domain 6 (TM6) is highly conserved and believed to participate in the catalytic function and conformational stability of V-PPase. In this study, alanine-scanning mutagenesis along TM6 of the mung bean V-PPase was carried out to identify its structural and functional role. Mutants Y299A, A306S and L317A exhibited gross impairment in both PPi hydrolysis and proton translocation. Meanwhile, mutations at L307 and N318 completely abolished the targeting of the enzyme, causing broad cytosolic localization and implicating a possible role of these residues in protein translocation. The location of these amino acid residues was on the same side of the helix wheel, suggesting their involvement in maintaining the stability of enzyme conformation. G297A, E301A and A305S mutants showed declines in proton translocation but not in PPi hydrolysis, consequently resulting in decreases in the coupling efficiency. These amino acid residues cluster at one face of the helix wheel, indicating their direct/indirect participation in proton translocation. Taken together, these data indicate that TM6 is crucial to vacuolar H+-pyrophosphatase, probably mediating protein targeting, proton transport, and the maintenance of enzyme structure.
AB - Vacuolar H+-pyrophosphatase (V-PPase; EC 3.6.1.1) plays a significant role in the maintenance of the pH in cytoplasm and vacuoles via proton translocation from the cytosol to the vacuolar lumen at the expense of PPi hydrolysis. The topology of V-PPase as predicted by TopPred II suggests that the catalytic site is putatively located in loop e and exposed to the cytosol. The adjacent transmembrane domain 6 (TM6) is highly conserved and believed to participate in the catalytic function and conformational stability of V-PPase. In this study, alanine-scanning mutagenesis along TM6 of the mung bean V-PPase was carried out to identify its structural and functional role. Mutants Y299A, A306S and L317A exhibited gross impairment in both PPi hydrolysis and proton translocation. Meanwhile, mutations at L307 and N318 completely abolished the targeting of the enzyme, causing broad cytosolic localization and implicating a possible role of these residues in protein translocation. The location of these amino acid residues was on the same side of the helix wheel, suggesting their involvement in maintaining the stability of enzyme conformation. G297A, E301A and A305S mutants showed declines in proton translocation but not in PPi hydrolysis, consequently resulting in decreases in the coupling efficiency. These amino acid residues cluster at one face of the helix wheel, indicating their direct/indirect participation in proton translocation. Taken together, these data indicate that TM6 is crucial to vacuolar H+-pyrophosphatase, probably mediating protein targeting, proton transport, and the maintenance of enzyme structure.
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U2 - 10.1016/j.bbabio.2010.10.006
DO - 10.1016/j.bbabio.2010.10.006
M3 - Article
C2 - 20937245
AN - SCOPUS:78249240582
VL - 1807
SP - 59
EP - 67
JO - Biochimica et Biophysica Acta - Bioenergetics
JF - Biochimica et Biophysica Acta - Bioenergetics
SN - 0005-2728
IS - 1
ER -