Enzymes have their cycles, catalytic ones: bind a substrate, catalyse some sort of reaction, release the product... then do it again. These cycles have memory effects: long turnover is likely to be followed by another long one, and short one is likely to be followed by another short one. This makes total sense: efficient act of catalysis is possible only when appropriate conformation is achieved and all the residues are aligned as they should be... and that is a recipe for one more efficient round!
Now let us look at RelA. Based on in vivo single molecule tracking investigations we recently proposed a model of RelA catalytic cycle: it sits on the ribosome, gets activated by arrival of deacylated tRNA to the A site, falls off and performs multiple acts of ppGpp synthesis from ATP and GDP. Importantly, RelA must go through the ribosome-bound stage in order to get activated. This seems to be an extreme cause of memory effects - while active off the ribosome, RelA remembers the activation event that happened on the ribosome!
It is quite a scary thought... what else does it remember? Does it remember the moment I started working on it? Well, surely not, even I don't remember that moment any more. Or may be I am just blocking out that memory.
References:
H. Peter Lu, Phys. Chem. Chem. Phys (2011), 13 pp. 6734-6749, PIMD 21409227
Brian P. English et al., PNAS (2011), 108(13) pp. E365-373, PIMD 21730169
Now let us look at RelA. Based on in vivo single molecule tracking investigations we recently proposed a model of RelA catalytic cycle: it sits on the ribosome, gets activated by arrival of deacylated tRNA to the A site, falls off and performs multiple acts of ppGpp synthesis from ATP and GDP. Importantly, RelA must go through the ribosome-bound stage in order to get activated. This seems to be an extreme cause of memory effects - while active off the ribosome, RelA remembers the activation event that happened on the ribosome!
It is quite a scary thought... what else does it remember? Does it remember the moment I started working on it? Well, surely not, even I don't remember that moment any more. Or may be I am just blocking out that memory.
References:
H. Peter Lu, Phys. Chem. Chem. Phys (2011), 13 pp. 6734-6749, PIMD 21409227
Brian P. English et al., PNAS (2011), 108(13) pp. E365-373, PIMD 21730169
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