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Structural basis for the subtype-selectivity of KCa2.2 channel activators
Miao Zhang1, Young-Woo Nam1, Alena Ramanishka1
1Chapman University.
Research Square
|June 5, 2025
Summary
Structural insights reveal how rimtuzalcap selectively activates small-conductance (KCa2.2) calcium-activated potassium channels, distinct from intermediate-conductance (KCa3.1) channels. This selectivity is key for developing new neurological disorder treatments.
Area of Science:
- Structural biology
- Molecular pharmacology
- Neuroscience
Background:
- Small-conductance (KCa2.2) and intermediate-conductance (KCa3.1) calcium-activated potassium channels are crucial regulators of cellular excitability.
- These channels are modulated by calcium and calmodulin, with specific drugs like NS309 and rimtuzalcap exhibiting differential effects.
- Rimtuzalcap shows therapeutic potential for neurological conditions such as spinocerebellar ataxia and essential tremor.
Purpose of the Study:
- To elucidate the structural basis for the subtype-selectivity of rimtuzalcap towards KCa2.2 channels.
- To understand the molecular mechanisms underlying the differential activation of KCa2.2 and KCa3.1 channels by NS309 and rimtuzalcap.
Main Methods:
- Cryo-electron microscopy (cryo-EM) was employed to determine high-resolution structures.
- Structures were obtained for KCa2.2 channels in complex with NS309 and rimtuzalcap.
- Structures were also determined for KCa3.1 channels bound to NS309.
Main Results:
- Distinct conformations of calmodulin and the cytoplasmic HC helices were observed between KCa2.2 and KCa3.1 channels.
- In KCa2.2, calmodulin's N-lobes adopt conformations accommodating both NS309 and rimtuzalcap.
- In KCa3.1, calmodulin's N-lobes are constrained by HC helices, allowing NS309 binding but precluding the bulkier rimtuzalcap.
Conclusions:
- The observed structural differences explain rimtuzalcap's selective activation of KCa2.2 channels.
- These findings provide a structural foundation for the rational design of subtype-selective KCa2.2 channel modulators.
- This work facilitates the development of novel therapeutics targeting KCa2.2-related neurological disorders.
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