A quantitative description of KcsA gating I: macroscopic currents.
The prokaryotic K(+) channel KcsA is activated by intracellular protons and its gating is modulated by transmembrane voltage. Typically, KcsA functions have been studied under steady-state conditions, using macroscopic Rb(+)-flux experiments and single-channel current measurements. These studies have provided limited insights into the gating kinetics of KcsA due to its low open probability, uncertainties in the number of channels in the patch, and a very strong intrinsic kinetic variability. In this work, we have carried out a detailed analysis of KcsA gating under nonstationary conditions by examining the influence of pH and voltage on the activation, deactivation, and slow-inactivation gating events. We find that activation and deactivation gating of KcsA are predominantly modulated by pH without a significant effect of voltage. Activation gating showed sigmoidal pH dependence with a pKa of approximately 4.2 and a Hill coefficient of approximately 2. In the sustained presence of proton, KcsA undergoes a time-dependent decay of conductance. This inactivation process is pH independent but is modulated by voltage and the nature of permeant ion. Recovery from inactivation occurs via deactivation and also appears to be voltage dependent. We further find that inactivation in KcsA is not entirely a property of the open-conducting channel but can also occur from partially "activated" closed states. The time course of onset and recovery of the inactivation process from these pre-open closed states appears to be different from the open-state inactivation, suggesting the presence of multiple inactivated states with diverse kinetic pathways. This information has been analyzed together with a detailed study of KcsA single-channel behavior (in the accompanying paper) in the framework of a kinetic model. Taken together our data constitutes the first quantitative description of KcsA gating.
Chakrapani
Sudha
S
Institute of Molecular Pediatrics Science, Department of Biochemistry and Molecular Biology, University of Chicago, Center for integrative Science, Chicago, IL 60637, USA.
Cordero-Morales
Julio F
JF
Perozo
Eduardo
E
D001426:Bacterial Proteins; D004594:Electrophysiology / Q000379:methods; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism; D017629:Gap Junctions; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating; D007477:Ions; D007700:Kinetics; D008564:Membrane Potentials; D008954:Models, Biological; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D011522:Protons; D013997:Time Factors
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D007477:Ions; C504448:KcsA protein, Streptomyces coelicolor; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011522:Protons