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Lecture 11

BIO304H5 Lecture Notes - Lecture 11: Osmotic Shock, Alpha Helix, Beta Sheet

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Adriano Senatore

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February 27th 2019
BIO304 Lecture 11 (2)
Regression on ion channel protein sequence
Ion channel properties arise from the physical properties of their constituent
amino acids - function is based on structure of protein
Different amino acids arranged in a sequence will promote different
secondary structures
e.g. alpha helices(alpha strands forming helices), beta strands
(piled up strands), disordered loops
Side groups of amino acids have different polarities and hence
Some amino acids have charges
Aspartate and glutamate
D & E are negatively charged
Histidine, lysine, arginine
H,K & R are positively charged - drive sensitivity voltage
As you would expect, TMHs contain mostly hydrophobic amino acids
Transmembrane helix - need to be able to make helix and amino acids
need to be hydrophobic
Remember the voltage sensor TMHs of Kv, Nav and Cav channels?
S4 helices contain:
Hydrophobic amino acids
Positively-charged lysine (K) and arginine (R) amino acids crucial
for voltage sensing
Ion channel properties arise from the physical properties of their constituent
amino acids
Secondary structures assemble into tertiary structures
This is the final "shape" of the folded subunit/protein
Subunits assemble into quaternary structures to make up functional
channels -- putting proteins together makes a channel - which is
quaternary structure
These are the protein complexes that make up a functional
channel unit
e.g. nAChR quaternary structure consists of 5 subunits
Sequence is very powerful in terms of proteins structure
Can look for homologues
Further cloning and gene sequencing efforts identified a large "superfamily" of Cys-loop
channels → some are cationic, some are anionic
Gamma aminobutyric acid (GABA) receptors
Anionic(conduct Cl-), found at inhibitory synapses (vertebrates and
Glycine receptors
Anionic, inhibitory synapses (vertebrates/chordates)
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