Some bacteria have two enzymes that do the same thing, albeit one is much more efficient than the other and at the same time at higher endogenous concentration as well.
Why would a bacteria would need two enzymes to do the same thing? Maybe at one point there was a divergent on the enzyme when it evolved, but became less active? Perhaps one is an evolutionary product of the other?
One example is dihydrofolate reductase - many flavors are found, often a few within the same bacteria. These can have resistance to trimethoprim but also reduced catalytic efficiency. Many are acquired by horizontal gene transfer.
Interestingly, trimethoprim is synthetic, yet even "virgin" ecologies have resistant populations and "resistant" DHFRs. Clearly something else must be going on!
One example is dihydrofolate reductase - many flavors are found, often a few within the same bacteria. These can have resistance to trimethoprim but also reduced catalytic efficiency. Many are acquired by horizontal gene transfer.
Interestingly, trimethoprim is synthetic, yet even "virgin" ecologies have resistant populations and "resistant" DHFRs. Clearly something else must be going on!
That's really interesting Christina. Do you have a reference for that? Perhaps there are natural microbial compounds that act in the same way trimethoprim. I think that it is interesting that some bacteria synthesise lots of folate and others need to get it from the environment. It must also be something to do with the ecology of the environment that they live in.
As an example of "natural" resistance - my favorite is
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0034953
Antibiotic Resistance Is Prevalent in an Isolated Cave Microbiome
although I think this group has shown similar profiles in other ecological niches.
It's also worth mentioning that for gram negatives trimethoprim is an efflux pump substrate (acinetobacter, bulkholderia, pseudomonas).
I'm not aware of bacteria that *need* to get folate from the environment (like we do!), but some seem to have salvage pathways (debated but perhaps E faecalis?) similar to what plants use??
Thanks for the reference. Most lactobacilli lack the ability to make folate. See reference below for links.
Article Folate Production by Probiotic Bacteria
The general explanation might be to have a resistance towards competitive inhibitors produced by surrounding organisms in the environment. High efficiency (low Km) for an enzyme is often accompanied by low specificity and the reverse (binding pocket is more choosy for a low efficiency enzyme and even the right substrate has some problem fitting). Christina Bourne's mentioned a perfect example of this in the dihydrofolate reductase. To carry a low efficiency (high selectivity) version of an enzyme could be a general "insurance policy" against encountering competitive inhibitors produced by other organisms in the environment while using the high efficient version under "normal" conditions. Especially important should this be for "essential" enzymes that when inhibited results in complete growth inhibition or death in a natural environment. In other words I would expect this situation for many "essential" enzymes and especially in bacterial strains recently isolated from the environment. Does anyone know of studies that could corroborate or disproof this expectation?
Many enzymes involved in fatty acid synthesis cycle are redundant as well, like ELO 1 - 4. I do believed that its a single enzyme right in the beginning, which gradually evolved to develop specialize traits ELO1 overlaps with ELO2, ELO2 overlaps with ELO3, ELO3 overlaps with ELO4, but ELO1 and ELO4 do not share similar activity significantly.
These are all very interesting stuff guys! and Choon I agree this seems to be very common in FAS cycle... very interesting!
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