title: Control of cell membrane ecto-ATPase by oligomerization state: intermolecular cross-linking modulates ATPase activity.
abstract: The extracellular ATPase (ecto-ATPase) is a divalent cation-dependent nucleoside triphosphatase with an unusually high specific activity. Monoclonal antibodies, described previously [Stout, J. G., Strobel, R. S., & Kirley, T. L. (1995) J. Biol. Chem. 270, 11845-11850], and newly generated polyclonal antibodies, both raised against the chicken gizzard ecto-ATPase, were evaluated for their ability to cross-react with mammalian ecto-ATPases and were used as specific immunochemical probes to identify non-cross-linked and cross-linked ecto-ATPase. Unlike previous results obtained with the rabbit skeletal muscle ecto-ATPase enzyme, cross-linking the chicken gizzard smooth muscle ecto-ATPase with 3,3'-dithiobis(sulfosuccinimidylpropionate) (DTSSP) and dithiobis(succinimidylpropionate) (DSP) increased the activity of the enzyme which corresponded to an increase in a approximately 130 kDa immunoreactive band, proposed to be a ecto-ATPase homodimer, and a concomitant decrease in a approximately 66 kDa immunoreactive band, the ecto-ATPase monomer. Ecto-ATPase was immunochemically identified in chicken, rat, mouse, rabbit, and pig. Interestingly, under nonreducing conditions, the ecto-ATPase activity in rat and pig (unlike chicken and rabbit) was evident on Western blots as an immunoreactive band at approximately 200 kDa, proposed to be an intermolecularly disulfide-linked ecto-ATPase homotrimer. Nonreducing Western blot analysis of various rat tissues with three different monoclonal antibodies that recognize the 66 kDa chicken gizzard ecto-ATPase monomer strengthened the hypothesis that this 200 kDa band indeed represents the trimeric ecto-ATPase. After reduction, ecto-ATPase monomers were found to be approximately 66 kDa in all species examined. The differences in ecto-ATPase quaternary structure stability may account for the observed species differences in ecto-ATPase enzymatic properties. Intermolecular disulfide bonds appear to be one of the species-specific ways to stabilize the native, active ecto-ATPase quaternary structure (the homotrimer). Based on the data obtained, as well as previous data from this and other laboratories, a hypothesis was developed to explain the modulation of ecto-ATPase activity by a variety of agents, including detergents, chemical cross-linkers, lectins, antibodies, and small molecule inhibitors. It is proposed that agents and conditions stabilizing ecto-ATPase oligomers stimulate enzyme activity, whereas agents and conditions destabilizing ecto-ATPase homooligomers would inhibit the ecto-ATPase.
authors.affiliation: Department of Pharmacology and Cell Biophysics, College of Medicine, University of Cincinnati, Ohio 45267-0575, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Stout
authors.forename: T L
authors.initials: TL
authors.lastname: Kirley
mesh_terms: D000251:Adenosine Triphosphatases / Q000276:immunology / Q000378:metabolism*; D000818:Animals; D000918:Antibody Specificity; D002462:Cell Membrane / Q000201:enzymology*; D002645:Chickens; D003432:Cross-Linking Reagents; D004789:Enzyme Activation; D005895:Gizzard, Avian / Q000201:enzymology*; D051379:Mice; D009130:Muscle, Smooth / Q000201:enzymology*; D011487:Protein Conformation; D051381:Rats; D013552:Swine
chemical_list: D003432:Cross-Linking Reagents; D000251:Adenosine Triphosphatases; C027201:ectoATPase