MSGID: 1:317/3 642f9c72   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Blind dating in bacteria evolution    
    Reconstructed protein sequences in cyanobacteria reveal that protein   
   interactions can evolve without direct selection pressure    
      
     Date:   
         April 6, 2023   
     Source:   
         Max-Planck-Gesellschaft   
     Summary:   
         A team of researchers reconstructed long-extinct proteins of a   
         UV protection system of cyanobacteria. The surprising result:   
         the proteins were already compatible with each other when they   
         first met. This discovery expands the knowledge horizon on the   
         rules of evolution.   
      
      
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   FULL STORY   
   ==========================================================================   
   Proteins are the key players for virtually all molecular processes   
   within the cell. To fulfil their diverse functions, they have to interact   
   with other proteins. Such protein-protein interactions are mediated by   
   highly complementary surfaces, which typically involve many amino acids   
   that are positioned precisely to produce a tight, specific fit between   
   two proteins.   
      
   However, comparatively little is known about how such interactions are   
   created during evolution.   
      
      
   ==========================================================================   
   Classical evolutionary theory suggests that any new biological feature   
   involving many components (like the amino acids that enable an interaction   
   between proteins) evolves in a stepwise manner. According to this   
   concept, each tiny functional improvement is driven by the power of   
   natural selection because there is some benefit associated with the   
   feature. However, whether protein- protein interactions also always   
   follow this trajectory was not entirely known.   
      
   Using a highly interdisciplinary approach, an international team led by   
   Max Planck researcher Georg Hochberg from the Terrestrial Microbiology in   
   Marburg have now shed new light on this question. Their study provides   
   definitive evidence that highly complementary and biologically relevant   
   protein-protein interactions can evolve entirely by chance.   
      
   Proteins cooperate in a photoprotection system The research team made   
   their discovery in a biochemical system that microbes use to adapt to   
   stressful light conditions. Cyanobacteria use sunlight to produce their   
   own food through photosynthesis. Since much light damages the cell,   
   cyanobacteria have evolved a mechanism known as photoprotection: if light   
   intensities become dangerously high, a light intensity sensor named   
   Orange Carotenoid Protein (OCP) changes its shape. In this activated   
   form, OCP protects the cell by converting excess light energy into   
   harmless heat. In order to return into its original state, some OCPs   
   depend on a second protein: The Fluorescence Recovery Protein (FRP)   
   binds to activated OCP1 and strongly accelerates its recovery.   
      
   'Our question was: Is it possible that the surfaces that allow these   
   two proteins to form a complex evolved entirely by accident, rather than   
   through direct natural selection?' says Georg Hochberg. 'The difficulty   
   is that the end result of both processes looks the same, so we usually   
   cannot tell why the amino acids required for some interaction evolved   
   -- through natural selection for the interaction or by chance. To tell   
   them apart, we would need a time machine to witness the exact moment in   
   history these mutations occurred, 'Georg Hochberg explains.   
      
   Luckily, recent breakthroughs in molecular and computational biology   
   has equipped Georg Hochberg and his team with a laboratory kind   
   of time machine: ancestral sequence reconstruction. In addition,   
   the light protection system of cyanobacteria, which is under study   
   in the group of Thomas Friedrich from Technische Universita"t Berlin   
   since many years, is ideal for studying the evolutionary encounter of   
   two protein components. Early cyanobacteria acquired the FRP proteins   
   from a proteobacterium by horizontal gene transfer. The latter had no   
   photosynthetic capacity itself and did not possess the OCP protein.   
      
   To work out how the interaction between OCP1 and FRP evolved, graduate   
   student Niklas Steube inferred the sequences of ancient OCPs and FRPs   
   that existed billions of years ago in the past, and then resurrected   
   these in the laboratory. After translation of the amino acid sequences   
   into DNA he produced them using E. coli bacterial cells in order to be   
   able to study their molecular properties.   
      
   A fortunate coincidence The Berlin team then tested whether ancient   
   molecules could form an interaction. This way the scientists could   
   retrace how both protein partners got to know each other. 'Surprisingly,   
   the FRP from the proteobacteria already matched the ancestral OCP of   
   the cyanobacteria, before gene transfer had even taken place. The mutual   
   compatibility of FRP and OCP has thus evolved completely independently   
   of each other in different species, says Thomas Friedrich. This allowed   
   the team to prove that their ability to interact must have been a happy   
   accident: selection could not plausibly have shaped the two proteins'   
   surfaces to enable an interaction if they had never met each other.   
      
   This finally proved that such interactions can evolve entirely without   
   direct selective pressure.   
      
   'This may seem like an extraordinary coincidence,' Niklas Steube   
   says. 'Imagine an alien spaceship landed on earth and we found that   
   it contained plug-shaped objects that perfectly fit into human-made   
   sockets. But despite the perceived improbability, such coincidences   
   could be relatively common. But in fact, proteins often encounter a   
   large number of new potential interaction partners when localisation or   
   expression patterns change within the cell, or when new proteins enter   
   the cell through horizontal gene transfer.' Georg Hochberg adds, 'Even   
   if only a small fraction of such encounters ends up being productive,   
   fortuitous compatibility may be the basis of a significant fraction of all   
   interactions we see inside cells today. Thus, as in human partnerships,   
   a good evolutionary match could be the result of a chance meeting of   
   two already compatible partners.'   
       * RELATED_TOPICS   
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                   # Cell_Biology # Molecular_Biology # Genetics   
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             o Fossils_&_Ruins   
                   # Evolution # Charles_Darwin # Fossils   
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             o Convergent_evolution o Heat_shock_protein o Protein o   
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   ==========================================================================   
   Story Source: Materials provided by Max-Planck-Gesellschaft. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Niklas Steube, Marcus Moldenhauer, Paul Weiland, Dominik Saman,   
      Alexandra   
         Kilb, Ada'n A. Rami'rez Rojas, Sriram G. Garg, Daniel Schindler,   
         Peter L.   
      
         Graumann, Justin L. P. Benesch, Gert Bange, Thomas Friedrich,   
         Georg K. A.   
      
         Hochberg. Fortuitously compatible protein surfaces primed allosteric   
         control in cyanobacterial photoprotection. Nature Ecology &   
         Evolution, 2023; DOI: 10.1038/s41559-023-02018-8   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230406130743.htm   
      
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