期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 285, 期 31, 页码 23655-23664出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M110.134916
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资金
- National Science Council, Republic of China [NSC 98-2627-M-007-002, NSC 98-2627-M-007-001, 97-2311-B-007-003-MY3, NSC 98-2627-M-007-003, NSC-98-2627-M-007-004]
Homodimeric H+-pyrophosphatase (H+-PPase; EC 3.6.1.1) is a unique enzyme playing a pivotal physiological role in pH homeostasis of organisms. This novel H+-PPase supplies energy at the expense of hydrolyzing metabolic byproduct, pyrophosphate (PPi), for H+ translocation across membrane. The functional unit for the translocation is considered to be a homodimer. Its putative active site on each subunit consists of PPi binding motif, Acidic I and II motifs, and several essential residues. In this investigation structural mapping of these vital regions was primarily determined utilizing single molecule fluorescence resonance energy transfer. Distances between two C termini and also two N termini on homodimeric subunits of H+-PPase are 49.3 +/- 4.0 and 67.2 +/- 5.7 angstrom, respectively. Furthermore, putative PPi binding motifs on individual subunits are found to be relatively far away from each other (70.8 +/- 4.8 angstrom), whereas binding of potassium and substrate analogue led them to closer proximity. Moreover, substrate analogue but not potassium elicits significant distance variations between two Acidic I motifs and two His-622 residues on homodimeric subunits. Taken together, this study provides the first quantitative measurements of distances between various essential motifs, residues, and putative active sites on homodimeric subunits of H+-PPase. A working model is accordingly proposed elucidating the distance variations of dimeric H+-PPase upon substrate binding.
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