CLC Channels

1
CLC Channels

• Chlorine Channels

2
CLC Channels are Everywhere

• Regulate resting potential of muscles
• Regulate electrical excitability (GABA receptor
  is a Cl- channel)
• Regulate cell size
• Regulate renal and intravascular ion transport
• Regulate pH in stomach cells (part of gastric HCl
  apparatus).

3
Structure

• Dimeric
• Double barreled
• Each barrel acts independently
• Each subunit has an antiparrellel dimer
  structure

4
Structure
Dutzler, et al.
5
Structure
Dutzler, et al.
6
Structure
Dutzler, et al.
7
Selectivity Filter

• Conducts Cl-, Br-, NO3-, I-
• Formed by partial charges (preventing tight
  binding of anion)
• Formed by N-terminal ends of alpha helixes
• This is the reason for the anti-parallel
  structure of the individual monomers

8
Selectivity Filter
Dutzler, et al.
9
Comparison to Other Channels

• Interface between monomers does not form the
  pores (as in alpha-hemolysin and gramicidin)
• Helices are tilted and do not span membrane
• Selectivity Filter
• Dielectric membrane barrier maybe less for anions
• K selectivity filter differs greatly

10
Current Measurements
Miller, et al.
11
Gating

• Two gating mechanism
• Slow gating
• Cooperative gating between barrels
• 10-60 s (Jentsch, et al.)
• Opened by hyperpolarization
• Fast gating
• Independent gating for each barrel
• 10 ms (Jentsch, et al.)
• Opened by depolarization

12
Slow Gating
Miller, et al.
13
Effect of Extracellular Cl-
Pusch, et al.
14
Two Binding Sites?

• One binding site on the intracellular side
• Binding site for the selectivity filter
• Another binding site on the extracellular side
• Binding site for fast gating
• Cl- on the extracellular side triggers gating

15
Fast Gating
Dutzler, et al.
16
What to do?

• Channel is closed!
• Perform MD simulations and use Essential
  Dynamics
• Model fast gating process
• Determine gating binding site
• Obtain open structure
• Model selectivity with other monovalent anions
• Do PNP calculations on open structure
• BD simulations of ion transport and gating

17
References

• Dutzler, et al. Nature. 415, 287 (2002)
• Jentsch, et al. Physiol. Rev. 82, 511 (2001)
• Maduke, et al. Annu. Rev. Biophys. Biomol.
  Struct. 29, 411 (2000)
• Miller, et al. Proc. Natl. Acad. Sci. USA. 81,
  2772 (1984)
• Pusch, et al. Nature. 373, 6514 (1995)