Update on Degradosome Function: The Importance of Location

Update on Degradosome Function: The Importance of Location

By Mike Gene; 2/25/05

A few years ago, I used some ID Thinking to come up with a testable hypothesis about the function of enolase (a glycolytic enzyme) as part of the degradosome [1].

Enolase functions in the degradosome as a prong that plugs the degradosome into the glycolytic pathway so that ATP generated by pyruvate kinase is then quickly channeled to the helicase to fuel its unwinding activity.

The logic was essentially this:

ID entails that these cellular processes are quite sophisticated. Consistent with this prediction is a quasi-solid state cell, where order is paramount and random processes are minimized. …… ID allows me to take a view of the cell more as a sophisticated, machine-like entity rather than a jury-rigged hodgepodge cobbled together by the Blind Watchmaker. This is because biomolecular engineering at the hands of an advanced intelligence is likely to express its intervention such that the products of design reflect a state that is elegantly coherent. The expectation of a jury-rigged hodgepodge makes more sense in light of non-teleological views, which begin with the random mess of the prebiotic soup and not the watch-type reality Paley once invoked.

So I begin to think that the degradosome could indeed reflect an originally designed state given its basic house-keeping role. If so, what is enolase doing there? A non-teleological view gives me no reason to expect a logical reason for it being there, as evolution doesn't have to be logical, in fact, it often simply jury-rigs hodgepodge things together. But if enolase was originally part of the degradosome, which in turn was originally designed, I expect a logical reason for it being there.

A paper has just recently been published that, for the first time, demonstrates one of the possible roles of enolase in degradosomal function [2]. My prediction apparently missed the bull’s eye, but not by too much.

Put simply, enolase function in the degradosome is connected to glucose transport into the cell via glycolysis. It had been previously determined that if you block glycolysis in its early stages, the mRNA for ptsG, which encodes the major glucose transporter, is rapidly degraded. This makes sense, as a cell that cannot efficiently metabolize glucose via glycolysis need not transport it into the cell and instead turn to other fuel sources. Morita et al. [2] were able to show that if you eliminate only the enolase component of the degradosome in a strain of bacteria where glycolysis is blocked, such that phosphosugars begin to accumulate inside the cell, the mRNA for the glucose transporter is not degraded. Such degradation, in response to shutting down glycolysis, depends on enolase function.

But how does enolase function of the degradosome actually interface with glucose transport? Morita et. al suggest:

“one possible mechanism by which enolase stimulates ptsG mRNA degradation would be to modulate the membrane localization of RNase E.”

Thus, my ID thinking that stresses location and order as important to function is supported. To get the degradosome to degrade the glucose transporter mRNA, you have to bring the degradosome to the proper area in an enolase-dependent manner. What’s more, the enolase function of the degradosome does interfaces with glucose transport, providing a connection between glycolysis and degradosome function. However, my original specific hypothesis of enolase helping to shuttle energy to the degradosome appears fatally wounded by the fact that enolase/degradosome activity target certain mRNA degradation only when glycolysis is shut down.

There is much more to the degradosome story and the regulation of glucose transport that in turn further underscores the theme of my prediction of “a quasi-solid state cell, where order is paramount and random processes are minimized.” I will thus add to this essay in the future.

1. http://www.idthink.net/biot/degrad/index.html

2. Morita, T., Kawamoto, H., Mizota, T., Inada, T., and Aiba, H. 2004. Enolase in the RNA degradosome plays a crucial role in the rapid decay of glucose transporter mRNA in the response to phosphosugar stress in E. coli. Mol. Micro. 54: 1063-1075.