ion channel structure and function Flashcards
Shaker, channel inactivation
What is the Shaker potassium channel and its genetic origin?
The Shaker potassium channel is encoded by the Shaker (Sh) gene in Drosophila (fruit flies). It plays a crucial role in neuronal activity, influencing behaviors such as movement and sleep.
What are the observable effects of mutations in the Shaker gene?
Mutant flies exhibit leg shaking when anesthetized, abnormal movements when unaesthetized, and have a shorter lifespan. They sleep for about one-third as much as wild-type flies but remain unimpaired by sleep deprivation.
What is the closest human homologue of the Shaker potassium channel?
KCNA3.
What experimental methods are used to investigate ion channels?
Patch-clamp electrophysiology: Measures ionic currents and channel activity.
Molecular biology: Techniques for analyzing gene expression and protein function.
Cryo-electron microscopy (cryo-EM) or X-ray crystallography: Methods for determining the structure of ion channels.
How do ion channels function in terms of gating?
Ion channels open and close in response to various stimuli (gating), which allows for the selective movement of ions across the membrane.
What role do animal toxins play in ion channel research?
Certain toxins can inhibit ion channels, providing insights into their function:
Tetrodotoxin (TTX) from pufferfish: Blocks sodium channels.
Charybdotoxin (CTX) from deathstalker scorpion: Blocks potassium channels.
W-agatoxin from funnel web spider: Blocks calcium channels by targeting voltage sensors.
What are the characteristics of ion channels?
Ion channels are specialized and selective for specific ions, allowing for controlled pathways for ion flux. Their gating mechanisms enable dynamic control in response to voltage changes, ligand binding, or mechanical stretch.
Describe the structure of the KCNQ1 potassium channel.
The KCNQ1 potassium channel consists of four alpha subunits and four beta subunits, contributing to its selectivity and gating properties.
How can the amino acid sequence of a protein inform its structure?
Analyzing the amino acid sequence helps predict protein structure based on side-chain properties. Hydrophobic residues suggest transmembrane regions, while polar or charged residues indicate interactions in aqueous environments.
What is the role of X-ray crystallography in studying ion channels?
X-ray crystallography is used to determine protein structures at atomic resolution by crystallizing samples. Limitations include the long time required for crystallization and potential damage to the protein structure.
What are the advantages of cryo-electron microscopy (cryo-EM)?
Cryo-EM captures proteins in their native state by freezing samples, allowing for near-atomic resolution and fast sample preparation. It can accommodate macromolecules of any size and better represents the protein’s natural conformation.
What is the significance of positively charged amino acid residues in ion channels?
Positively charged residues (e.g., arginine and lysine) are crucial for ion selectivity and gating. They influence which ions can pass through the channel and play a role in channel opening and closing mechanisms.
Describe the two types of inactivation mechanisms in ion channels.
N-type inactivation: Involves amino acids at the N-terminus occluding the channel pore, leading to rapid inactivation that can be quickly reversed.
C-type inactivation: Characterized by conformational changes at the selectivity filter or extracellular entrance, resulting in slower inactivation and recovery. This mechanism can hinder action potentials and pain transmission.
