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SUMMARY:Transport mechanism and membrane interactions of the cation pumps 
 - Poul Nissen\, Aarhus University\, Denmark
DTSTART:20110217T161500Z
DTEND:20110217T180000Z
UID:TALK29734@talks.cam.ac.uk
CONTACT:Scientific Meetings Co-ordinator
DESCRIPTION:Danish National Research Foundation\, Center for Membrane Pump
 s in Cells and Disease – PUMPKIN. Department of Molecular Biology\, Aarh
 us University\, Denmark\, DK – 8000 Aarhus C\nP-type ATPases encompass t
 he cation pumps like Na+\,K+-ATPase and Ca2+-ATPase. They couple the trans
 port and countertransport of ions\, through a membrane spanning domain\, t
 o ATP hydrolysis via formation and breakdown of a phosphoenzyme intermedia
 te at cytoplasmic domains. The enzymes undergo large conformational change
 s where half-channels open and close\, and where the ion binding sites at 
 the middle of the membrane switch their specificity and orientation (Møll
 er 2010). Worth noting\, these large-scale movements take place in close i
 nteraction with the membrane.\nWe study P-type ATPases by interdisciplinar
 y approaches ranging from crystal structures to model organisms. \nNa+\,K+
 -ATPase is of key importance in animal cells and physiology. The enzyme tr
 ansports three sodium ions out and two potassium in per ATPase cycle. From
  the crystal structure of the pig kidney enzyme in the potassium-bound for
 m - further probed by mutagenesis and fast-kinetics - we pinpointed a key 
 role of the alpha subunit C-terminus\, and specifically on sodium binding 
 (Morth et al. 2007). The underlying mechanisms however remained elusive. F
 urthermore\, the uneven and electrogenic transport stoichiometry leads to 
 fundamental questions of how an unoccupied site is accounted when releasin
 g sodium and switching to potassium countertransport. \nUsing electrophysi
 ology\, MD simulations and structural analysis we have reached a new model
  of Na+\,K+-ATPase function: A C-terminal ion pathway\, plugged by the C-t
 erminus\, leads to the ion binding sites at the conserved Asp926 residue (
 pig alpha1 isoform\, Asp930 in human alpha2 isoform) which in the potassiu
 m-bound state becomes protonated (Poulsen et al. 2010). Through this chann
 el the proton can again return to the cytoplasm upon sodium binding\, thus
  ensuring that the overall 3:2 transport mechanism becomes electrogenic. T
 he importance is further underscored by a large cluster of mutations at th
 e C-terminal region associated with neurological diseases\, e.g. familial 
 hemiplegic migraine 2 (FHM2) and rapid-onset dystonia with parkinsonism (R
 DP).\nA low resolution crystal structure of the phosphorylated E2P form of
  the Na+\,K+-ATPase in complex with the cardiotonic steroid ouabain shows 
 conformational changes that not only explain the mechanism of inhibition\,
  but also hints at the possible role of these steroids in signaling with N
 a+\,K+-ATPase working as a receptor (Yatime et al. 2010).\nIn favourable c
 rystal forms of the related Ca2+-ATPase we have observed electron density 
 for lipid-detergent bilayers between molecules and we compare this experim
 ental basis to molecular dynamics simulations and biochemical/biophysical 
 data on the protein-lipid interaction thus to address a working transport 
 process across a membrane (Sonntag et al. submitted).¨\nCu(I)-ATPases con
 stitute another important P-type ATPase subfamily. We have determined the 
 first crystal structure of a Cu(I)-ATPase in a copper released state provi
 ding critical new insight on the copper transport pathway (Gourdon et al. 
 submitted).\n\nReferences:\nMorth JP\, Pedersen BP\, Toustrup-Jensen M\, A
 ndersen JP\, Vilsen B\, Nissen P (2007). Crystal structure of the sodium-p
 otassium pump. Nature 450\, 1043-1049\nMøller JV\, Olesen C\, Winther AM\
 , Nissen P (2010). The sarcoplasmic Ca2+-ATPase: design of a perfect chemi
 -osmotic pump. Q Rev Biophys. 2010 Sep 1:1-66 (epub ahead of print)\nPouls
 en H\, Khandelia H\, Morth JP\, Bublitz M\, Mouritsen OG\, Egebjerg J\, Ni
 ssen P (2010). Neurological disease mutations compromise a C-terminal ion 
 pathway in the Na(+)/K(+)-ATPase. Nature 467\, 99-102\nYatime L\, Laursen 
 M\, Morth JP\, Esmann M\, Nissen P\, Fedosova NU (2010). Structural insigh
 ts into the high affinity binding of cardiotonic steroids to the Na(+)\,K(
 +)-ATPase. J. Struct. Biol. 2010 Dec. 20 (epub ahead of print)\n
LOCATION:Max Perutz Lecture Theatre\, Medical Research Council (MRC) (MRC 
 Laboratory of Molecular Biol
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