Adenylate kinase-independent thiamine triphosphate accumulation under severe energy stress in Escherichia coli.
BACKGROUND
Thiamine triphosphate (ThTP) exists in most organisms and might play a role in cellular stress responses. In E. coli, ThTP is accumulated in response to amino acid starvation but the mechanism of its synthesis is still a matter of controversy. It has been suggested that ThTP is synthesized by an ATP-dependent specific thiamine diphosphate kinase. However, it is also known that vertebrate adenylate kinase 1 catalyzes ThTP synthesis at a very low rate and it has been postulated that this enzyme is responsible for ThTP synthesis in vivo.


RESULTS
Here we show that bacterial, as vertebrate adenylate kinases are able to catalyze ThTP synthesis, but at a rate more than 106-fold lower than ATP synthesis. This activity is too low to explain the high rate of ThTP accumulation observed in E. coli during amino acid starvation. Moreover, bacteria from the heat-sensitive CV2 strain accumulate high amounts of ThTP (>50% of total thiamine) at 37 degrees C despite complete inactivation of adenylate kinase and a subsequent drop in cellular ATP.


CONCLUSIONS
These results clearly demonstrate that adenylate kinase is not responsible for ThTP synthesis in vivo. Furthermore, they show that E. coli accumulate large amounts of ThTP under severe energy stress when ATP levels are very low, an observation not in favor of an ATP-dependent mechanisms for ThTP synthesis.
Gigliobianco
Tiziana
T
Center for Cellular and Molecular Neurobiology, University of Liège, Liège, Belgium. t.gigliobianco@ulg.ac.be
Lakaye
Bernard
B
Makarchikov
Alexander F
AF
Wins
Pierre
P
Bettendorff
Lucien
L
D000255:Adenosine Triphosphate / Q000378:metabolism; D000263:Adenylate Kinase / Q000302:isolation & purification / Q000378:metabolism*; D004734:Energy Metabolism; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D007527:Isoenzymes; D013217:Starvation; D013838:Thiamine Triphosphate / Q000378:metabolism*
D007527:Isoenzymes; D013838:Thiamine Triphosphate; D000255:Adenosine Triphosphate; D000263:Adenylate Kinase; C110939:adenylate kinase 1