The acidocalcisome inositol-1,4,5-trisphosphate receptor of Trypanosoma brucei is stimulated by luminal polyphosphate hydrolysis products
Year: 2019
Type: article
Abstract: Acidocalcisomes are acidic calcium stores rich in polyphosphate (polyP) and are present in trypanosomes and also in a diverse range of other organisms. Ca 2+ is released from these organelles through a channel, inositol 1,4,5-trisphosphate receptor (TbIP 3 R), which is essential for growth and infectivity of the parasite Trypanosoma brucei . However, the mechanism by which TbIP 3 R controls Ca 2+ release is unclear. In this work, we expressed TbIP 3 R in a chicken B lymphocyte cell line in which the genes for all three vertebrate IP 3 Rs were stably ablated (DT40–3KO). We show that IP 3 -mediated Ca 2+ release depends on Ca 2+ but not on ATP concentration and is inhibited by heparin, caffeine, and 2-aminomethoxydiphenyl borate (2-APB). Excised patch clamp recordings from nuclear membranes of DT40 cells expressing only TbIP 3 R disclosed that luminal inorganic orthophosphate (P i ) or pyrophosphate (PP i ), and neutral or alkaline pH can stimulate IP 3 -generated currents. In contrast, polyP or acidic pH did not induce these currents, and nuclear membranes obtained from cells expressing rat IP 3 R were unresponsive to polyP or its hydrolysis products. Our results are consistent with the notion that polyP hydrolysis products within acidocalcisomes or alkalinization of their luminal pH activate TbIP 3 R and Ca 2+ release. We conclude that TbIP 3 R is well-adapted to its role as the major Ca 2+ release channel of acidocalcisomes in T. brucei.
Source: Journal of Biological Chemistry
Institution: University of Georgia
Language: English
Subfield: Physiology
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
OpenAlex ID: W2947871760