|
Author
|
Topic: Archaeal ATPase indicates these enzymes evolved as chimeras
|
Doubting Thomas
Member
Member # 1214
|
posted 25. March 2004 14:07
A very recent publication in the Journal of Biological Chemistry (see next post for bibliographic info. pdf file requires use of free Adobe Acrobat reader. The article itself can be downloaded for free from JBC's web site.) brings out some very interesting information about the archaeal A1Ao ATPase that is evidence that ATPases both evolved from simpler proteins and are chimeric in nature, i.e. consisting of a complex of two proteins with different functions and origins.
In the article entitled Three-dimensional organization of the archaeal A1 ATPase from Methanosarcina mazei Gdelta1 by workers at several universities in Germany and the United States and just published last month, the authors state as follows on page 4:
quote:
INTRODUCTION - Methanogenic, halophilic and thermophilic archaea synthesize adenosine 5'-triphosphate (ATP) by means of ion gradient-driven phosphorylation. Although it was speculated for some time, due to the lack of in-depth information, that the ATP synthases of archaea may be either F1Fo- or V1Vo-like enzymes, it is now clear that they evolved as a sewparate class of ATPases/ATPsynthases, the A1Ao ATPsynthases/ases (1-4). This class of enzyme is different from F1Fo- or V1Vo-ATPases by function, subunit composition, regulation and structure (1). The A1Ao ATPase has at least nine subunits (A3:B3:C:D:E:F:H:I:Ksubx), but the actual subunit stoichiometry, especially regarding the proteolipid subunits K in A-ATPases (subunits c in F1Fo-ATPases) is different in various organisms (12, 6, 4 or, as suggested by genomic data, only 1 (5). As suggested by its bipartite name, the A1Ao ATPase is composed of a water-soluble A1 ATPase and an integral membrane complex, Ao. ATP is synthesized or hydrolyzed on the A1 headpiece, consisting of an A3B3 domain, and the energy provided for or released during that process is transmitted to the membrane-bound Ao domain (1). The energy coupling between the two active domains occurs via the so-called stalk part, an assembly proposed to be composed by the subunits C, D and F (2). The archaeal A1Ao ATP synthase/ase is regarded as a chimeric (italics mine) protein in which the membrane domain is closely related to the F1Fo ATP synthases but the catalytic subunits closely to V1Vo ATPases (3-4).
As I posted in another thread, the various ATP synthases that we see today are not examples of primordial systems from the beginning of life but instead the result of their modification and adaptation through subsequent billions of years of evolution. The '1' domains started out as simple soluble ATPases, then became more efficient hexameric A3B3 ATPases via gene duplication and divergence, such as we see in the globins. The 'o' domains started out as ion channels. In the genetics of these organisms, the 'o' domains are made first, before the '1' domains. The '1' domains are made after the 'o' domains are completed, and 'pop' into them and stay put through hydrophobic bonding. If this were not the case, the water-soluble '1' domains would simply (and ineffectively) diffuse off into the cytoplasm. The 'o's and the '1's started out as separate entities with different functions but ultimately linked up to result in an efficient producer of ATP.
The rotary action of these enzymes is powered by and is the inevitable result of the proton flux through the enzyme. A simple analogy is the familiar rotary lawn sprinkler. High pressure water goes in and the thing spins. Not quite the same mechanism in the ATPases, but you get the general idea. The force of the proton flux (the 'proton motive force') causes the '1' domain to spin by converting an electrical potential into rotational movement.
The example discussed in this paper is clear evidence of a much more complex evolutionary history for these proteins than is usually assumed. The scenario outlined above is a reasonable explanation of how a supposedly IC protein could have evolved in a stepwise Darwinian manner.
[ 25. March 2004, 18:10: Message edited by: Doubting Thomas ]
IP: Logged
|
|
Doubting Thomas
Member
Member # 1214
|
posted 25. March 2004 14:12
That web page URL doesn't work for some reason, so here is the bibliographic info for the paper I cited:
J Biol Chem. 2004 Feb 26 [Epub ahead of print]
Three-dimensional organization of the archaeal A1 ATPase from methanosarcina mazei Gdelta 1.
Coskun U, Radermacher M, Muller V, Ruiz T, Gruber G.
Fachrichtung 2.5 - Biophysik, Universitt des Saarlandes, Homburg D-66421.
IP: Logged
|
|
Moderator
Administrator
Member # 1
|
posted 25. March 2004 19:00
This post is being moved to "Literature Review"
IP: Logged
|
|
|
Topic Closed
Printer-friendly view of this topic