Role of the potassium/lysine cationic center in catalysis and functional asymmetry in membrane-bound pyrophosphatases.

Membrane-bound pyrophosphatases (mPPases), which couple pyrophosphate hydrolysis to transmembrane transport of H and/or Na ions, are divided into K,Na-independent, Na-regulated, and K-dependent families. The first two families include H-transporting mPPases (H-PPases), whereas the last family comprises one Na-transporting, two Na- and H-transporting subfamilies (Na-PPases and Na,H-PPases, respectively), and three H-transporting subfamilies. Earlier studies of the few available model mPPases suggested that K binds to a site located adjacent to the pyrophosphate-binding site, but is substituted by the ε-amino group of an evolutionarily acquired lysine residue in the K-independent mPPases.

Two independent evolutionary routes to Na+/H+ cotransport function in membrane pyrophosphatases.

Membrane-bound pyrophosphatases (mPPases) hydrolyze pyrophosphate (PPi) to transport H(+), Na(+) or both and help organisms to cope with stress conditions, such as high salinity or limiting nutrients. Recent elucidation of mPPase structure and identification of subfamilies that have fully or partially switched from Na(+) to H(+) pumping have established mPPases as versatile models for studying the principles governing the mechanism, specificity and evolution of cation transporters. In the present study, we constructed an accurate phylogenetic map of the interface of Na(+)-transporting PPases (Na(+)-PPases) and Na(+)- and H(+)-transporting PPases (Na(+),H(+)-PPases), which guided our experimental exploration of the variations in PPi hydrolysis and ion transport activities during evolution.

Evolutionarily divergent, Na+-regulated H+-transporting membrane-bound pyrophosphatases.

Membrane-bound pyrophosphatase (mPPases) of various types consume pyrophosphate (PPi) to drive active H+ or Na+ transport across membranes. H+-transporting PPases are divided into phylogenetically distinct K+-independent and K+-dependent subfamilies. In the present study, we describe a group of 46 bacterial proteins and one archaeal protein that are only distantly related to known mPPases (23%-34% sequence identity).

Membrane Na+-pyrophosphatases can transport protons at low sodium concentrations.

Membrane-bound Na(+)-pyrophosphatase (Na(+)-PPase), working in parallel with the corresponding ATP-energized pumps, catalyzes active Na(+) transport in bacteria and archaea. Each ~75-kDa subunit of homodimeric Na(+)-PPase forms an unusual funnel-like structure with a catalytic site in the cytoplasmic part and a hydrophilic gated channel in the membrane. Here, we show that at subphysiological Na(+) concentrations (<5 mM), the Na(+)-PPases of Chlorobium limicola, four other bacteria, and one archaeon additionally exhibit an H(+)-pumping activity in inverted membrane vesicles prepared from recombinant Escherichia coli strains.

Pyrophosphate-fueled Na+ and H+ transport in prokaryotes.

In its early history, life appeared to depend on pyrophosphate rather than ATP as the source of energy. Ancient membrane pyrophosphatases that couple pyrophosphate hydrolysis to active H(+) transport across biological membranes (H(+)-pyrophosphatases) have long been known in prokaryotes, plants, and protists. Recent studies have identified two evolutionarily related and widespread prokaryotic relics that can pump Na(+) (Na(+)-pyrophosphatase) or both Na(+) and H(+) (Na(+),H(+)-pyrophosphatase).