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UID:DSC-12507
DTSTART;TZID=Europe/Berlin:20170301T110000
SEQUENCE:1488441353
TRANSP:OPAQUE
DTEND;TZID=Europe/Berlin:20170301T120000
URL:https://dresden-science-calendar.de/calendar/en/detail/12507
LOCATION:MPI-CBG\, Pfotenhauerstraße 10801307 Dresden
SUMMARY:Mulkidjanian: Ancient Systems of Na+/K+ Homeostasis as Predecessors
  of Membrane Bioenergetics
CLASS:PUBLIC
DESCRIPTION:Speaker: Armen Y. Mulkidjanian\nInstitute of Speaker: School of
  Physics\, University of Osnabrueck\, Germany\; School of Bioengineering a
 nd Bioinformatics and A.N. Belozersky Institute of Physico-chemical Biolog
 y\, Lomonosov Moscow State University\, Russia\nTopics:\nBiologie\n Locati
 on:\n  Name: MPI-CBG (Seminar room Galleria)\n  Street: Pfotenhauerstraße
  108\n  City: 01307 Dresden\n  Phone: +49 351 210-0\n  Fax: +49 351 210-20
 00\nDescription: It is well known that the cytoplasm of living cells\, gen
 erally\, contains more potassium ions than sodium ions. It is also well es
 tablished that prevalence of K+ ions is crucial for the activity of numero
 us (nearly) universal key enzymes\, including those components of the tran
 slation system that even preceded the Last Universal Cellular Ancestor (LU
 CA) [1].  The inhibitory effect of Na+ on many of these ubiquitous K+-depe
 ndent enzymes does not seem compatible with the evolution of the ancestral
  cellular systems in marine environments with high sodium levels. Based on
  the data on the prevalence of potassium over sodium in cellular tissues\,
  Archibald Macallum suggested\, as early as in 1926\, that the first cells
  might have emerged in K+-rich habitats [2].   Different\, albeit compleme
 ntary\, scenarios have been recently proposed for the primordial K+-rich e
 nvironments based on experimental data and theoretical considerations [1\,
 3]. Specifically\, building on the observation that the [K+]/[Na+] ratio i
 s much greater than unity at vapor-dominated zones of inland geothermal sy
 stems\, we argued that the first cells could have emerged in the pools and
  puddles at the periphery of primordial anoxic geothermal fields\, where t
 he elementary composition of the condensed vapor would resemble the intern
 al milieu of modern cells [1].  Marine environments generally show a [K+]/
 [Na+] << 1.0. Therefore\, to invade such environments\, while maintaining 
 the cytoplasmic [K+]/[Na+] ratio over unity\, primordial cells needed ion-
 tight membranes and means to extrude sodium ions. The foray into marine\, 
 Na+-rich habitats was likely to drive the evolution of diverse redox-\, li
 ght-\, chemically-\, or osmotically-dependent sodium export pumps as well 
 as the increase of membrane tightness [4\,5]. At some point\, under the co
 nditions of high salinity of the primordial ocean\, one of such pumps\, th
 e Na+-translocating rotary ATPase\,  could change the direction of rotatio
 n and start to synthesize ATP at the expense of the transmembrane sodium p
 otential\, thus launching the membrane bioenergetics. In a rotary ATP synt
 hase the energy of sequentially translocated ions is stored stepwise in th
 e elastic deformation of the enzyme until enough energy to drive ATP synth
 esis is accumulated [6]. Hence\, the rotary ATP synthase is a unique machi
 ne that can synthesize ATP by accumulating small portions of energy\, whic
 h could be harvested by diverse redox- or light-driven ion translocases [5
 \,7].  Furthermore\, the rotary ATP synthases could be driven even by expe
 lling “garbage” out of the cell - when the expelled cation(s) is/are a
 ccompanied with anionic forms of the end-products of cell fermentation\, s
 uch as acetate or lactate [8\,9]. Hence\, on the primordial anoxic Earth\,
  where organic acids should have been the end-products in most of prokaryo
 tic fermentation pathways\, a part of the ATP stock could be synthesized (
 almost) “for free” [5]. After the oxygenation of the atmosphere\, the 
 enzymes of membrane bioenergetics gradually became decoupled from the mach
 inery responsible for maintaining the Na+/K+ disequilibrium. On one hand\,
  prokaryotic membranes became largely impermeable not only to sodium ions 
 but also to protons\, and the proton-dependent bioenergetics\, more benefi
 cial under oxidizing conditions [10]\, became prevalent. On the other hand
 \, the ancestors of eukaryotes\, on one hand\, evolved a specialized\, ext
 remely efficient enzyme to maintain the Na+/K+ disequilibrium\, namely the
  Na+/K+ ATPase\, and\, on the other hand\, recruited &amp\;#945\;-proteoba
 cteria as energy-converting machines\, future mitochondria.  Still\, eukar
 yotic cells harbor a plethora of Na+-coupled membrane enzymes\, including 
 the G-protein coupled receptors [11]\, as relics of the primordial Na+-exp
 orting machinery.
DTSTAMP:20260406T111519Z
CREATED:20170210T075940Z
LAST-MODIFIED:20170302T075553Z
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