8 - TA Christine Feng [email protected] Section Mon 4-5...

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TA: Christine Feng [email protected] Section: Mon 4-5 Center 205 OH: Wed 11-12 Geisel S&E This Week In Lecture: K+ Channel Bacterial Photosynthetic Reaction Center Light Harvesting Particles Example: β adrenergic receptor (PDB – 2RH1) K+ Channel Highly selective for K+ (1.35Å) ions even though Na+ is smaller (.95Å) o K+ coordinated by 8 H 2 0, Na+ by 6 H 2 0 Strong interactions between K+ & selectivity filter pore o Made of 4 monomers - 2 transmembrane α -helices, 1 pore helix, and a cytosolic tail. Selectivity Filter formed from the backbone o Carbonyl oxygens from the loops connecting pore helix to inner transmembrane helix. o Bind to dehydrated K+ ions (lose water hydration shell) – compensates for energy cost of dehydration o Dimensions of binding sites very exact so K+ ions fit precisely o Oxygen atoms are not close together enough to equalize the cost for dehydration of Na+ o K+ ion entering filter will repel ion already in filter Bacterial Photosynthetic Reaction Center
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8 - TA Christine Feng [email protected] Section Mon 4-5...

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