Biophysical studies of membrane proteins/peptides. Interaction with ...

BINDING OF INHIBITORS TO A PUTATIVE BINDING
DOMAIN OF V-ATPase
In eukaryotic cells, V-ATPase, apart from being present in the plasma membrane of
osteoclasts and kidney acid secreting cells, is also found in many organelles such as
vacuoles, lysossomes, coated vesicles, Golgi, and secretory vesicles. Numerous
physiological processes depend on the activity of V-ATPases, including intracellular
targeting, protein processing, transport of metabolites, receptor-mediated endocytosis,
neurotransmitter uptake, and apoptosis (Finbow and Harrison, 1997; Nishi and Forgac,
2002).
The macrolide antibiotics bafilomycins and concanamycins are specific, highly
potent inhibitors of all eukaryotic V-ATPases in vitro and in vivo (Fig. III-3). However,
their unselective action towards V-ATPases turns them to be extremely toxic agents and
unsuitable for therapeutical use in osteoporosis treatment (Dröse and Altendorf, 1997).
Recently, novel and selective inhibitors of osteoclasts V-ATPase have been synthesized
according to structure-function relationships of bafilomycins derivatives (Gagliardi et
al., 1998a; Gagliardi et al. 1998b), suggesting that selective modulation of different V-
ATPases might be possible by this new indole class of inhibitors, namely by its most
promising representative SB 242784 (INH-3) (see Fig. III.3) (Nadler et al., 1998). SB
242784 studies with animal models of bone resorption showed a remarkable efficiency
in the prevention of ovariectomy-induced bone loss on rats, and no adverse effects of its
administration on the animals was observed. In situ studies revealed that SB 242784
inhibited osteoclastic V-ATPase activity at 1000 times smaller concentrations than
enzymes from any other tissue evaluated (Visentin et al., 2000).
Figure III-3: V-ATPase inhibitors.
81