A light-driven sodium ion pump in marine bacteria
Light-driven proton-pumping rhodopsins are
widely distributed in many microorganisms. For example, proteorhodopsin is a
membrane protein that contains retinal, during light absorption conformational
changes cause protons to be transported across a membrane. This results in an
electrochemical gradient across the membrane, which is utilized in ATP
synthesis serving as an energy source of the cell.
Keiichi Inoue et al (2013) describe a new functional class of a microbial rhodopsin, a
light-driven sodium ion pump. They found that flavobacterium Krokinobacter eikastus possesses two
rhodopsins, KR1 and KR2.
KR1 is a ‘classic’ proton pump, and likely
plays a role similar to that of proteorhodopsin, (as described above). However
the work conducted by Keiichi Inoue and friends (2013)
describes KR2 as being able to pump sodium ions ‘outward’. In addition to
functioning as a sodium pump KR2 has the ability to act as a pump for lithium
ions as well. However when presented with potassium chloride or salts from
larger cations it converts to a proton pump.
The data presented in this study is
indicative that KR2 is a compatible sodium ion-proton pump. Additionally spectroscopic
analysis revealed that binds sodium ions in its extracellular domain. The
authors put forward that these findings are suggestive of light-driven sodium
pumps being equally important in situ as
their proton-pumping counterparts.
This research conducted by Keiichi
Inoue et al (2013) is not only interesting, but additionally valuable as it
builds on previous work done on other flavobacteria making the
discoveries found here comparable. Again it’s interesting how far research in this area has come
sine the work conducted by Beja et al (2001).
Sean, this is fantastic. This paper directly answers a problem identified by me in one of my previous blogs "a new type of bacterial rhodopsin"
ReplyDelete(http://biol3309-2012.blogspot.co.uk/20 13/01/a-new-type-of-bacterial-rhodopsin.html).
I identified that we did not know enough about some of the functions of Bacterial Rhodopsins to speculate their functions in the flavobacteria. they made some speculative suggestions for function in my blog but here, this study you have done for your blog appears to shed some light on the functionality which can enable us to improve our understanding of the significance of this protein in flavobacteria
Thanks James!
ReplyDeleteI remember enjoying reading your blog! isn't it great how Kwon et al were able to almost predict this. How has this paper effected your original conclusions?
It is clear that our understanding is improving significantly with the availability of genomic techniques. Kwon et al were just able to identify the new rhodopsins expression in NaCl concerntrations which in my opinoun does not provide much of a basis for its function but coupled with studies like this, that understanding of the function has become a lot clearer
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