Atomic determinants of BK channel activation by polyunsaturated fatty acids

Abstract

Docosahexaenoic acid (DHA), a polyunsaturated ω-3 fatty acid enriched in oily fish, contributes to better health by affecting multiple targets. Large-conductance Ca 2+ -and voltage-gated Slo1 BK channels are directly activated by nanomolar levels of DHA. We investigated DHA-channel interaction by manipulating both the fatty acid structure and the channel composition through the site-directed incorporation of unnatural amino acids. Electrophysiological measurements show that the para-group of a Tyr residue near the ion conduction pathway has a critical role. To robustly activate the channel, ionization must occur readily by a fatty acid for a good efficacy, and a long nonpolar acyl tail with a Z double bond present at the halfway position for a high affinity. The results suggest that DHA and the channel form an ion-dipole bond to promote opening and demonstrate the channel druggability. DHA, a marine-derived nutraceutical, represents a promising lead compound for rational drug design and discovery. -4,7,10,13,16,19-hexaenoic acid], found abundantly in oily fish, are believed to have many health-promoting effects (1). For example, select ω-3 PUFAs may decrease cardiovascular disease risk (2). Furthermore, human studies suggest that ω-3 PUFAs may lower blood pressure in some individuals (3). Thus, PUFAs such as DHA are natural nutraceuticals with great potential as lead compounds for rational drug design and discovery. To be successful, such an effort requires clear mechanistic understanding of the interactions between PUFAs and their effectors (4); however, the molecular targets of PUFAs and the mechanisms of action are only beginning to be revealed.One of the high-affinity targets of PUFAs is the large-conductance Ca 2+ -and voltage-gated K + (Slo1 BK) channel (5), whose activation in vascular smooth muscle cells facilitates vessel relaxation (6). Vascular Slo1 BK channels made of four pore-forming Slo1 and auxiliary β1 subunits (Slo1 + β1) are potently and reversibly activated by DHA with a nanomolar level of EC 50 , and this effect contributes to the hypotensive action of DHA in wild-type mice but not in mice with the gene encoding the channel (KCNMA1) disrupted (5).The function of the Slo1 BK channel can be electrophysiologically monitored with high precision to produce quantitative results amenable to mechanistic interpretations (7,8). Such in vitro studies show that DHA biases the ion conduction gate of the channel toward the open conformation without any need for activation of the channel's Ca 2+ sensors in the intracellular domain or transmembrane voltage sensor domains (VSDs) (5). Structurally, the action of DHA depends on a Tyr residue [Y318 in human Slo1 (hSlo1)] near the intracellular end of the ion conduction pathway; the mutation Y318S abolishes the activating effect of DHA (9).The exact role of Y318 in mediating the effect of DHA, however, is not clear. Some clues may be gained from interactions of other proteins with PUFAs. Extracellular DHA regulates voltagegated K + channels by interacting with ...

Polyunsaturated fatty acids produce a range of activators for heterogeneous IKs channel dysfunction

“…The pH dependence of PUFA head group ionization was also shown in the Slo1 BK channel by Tian et al (2016). They found that DHA produces potent activation of Slo1 BK channels and that this effect can be reduced when the pH is decreased, leading to protonation of the PUFA head group, and that the effect can be potentiated when the pH is increased, leading to deprotonation of the PUFA head group (Tian et al, 2016).…”

Large-conductance Ca 2+ - and voltage-gated K + channels form and break interactions with membrane lipids during each gating cycle

“…The membrane phospholipid-dependent gating cycle model of Slo1 may be helpful in understanding how the channel gating is influenced by diverse amphipathic molecules such as PIP 2 (14)(15)(16), hemin (29), and omega-3 docosahexaenoic acid (30). One aspect of the PIP 2 action involves the RKK segment (14,16), and intracellular PIP 2 may compete with E321 and E324 for ion-ion interactions with 329 RKK 331 , destabilizing the closed conformation.…”

ω‐6 and ω‐9 polyunsaturated fatty acids with double bonds near the carboxyl head have the highest affinity and largest effects on the cardiac IKs potassium channel

“…Tian et al, applied PUFAs, such as DHA (22:6Δ4,7,10,13,16,19), onto Slo1‐β1 BK channels to determine the important features for PUFAs to interact with BK channels. They concluded that double bonds at least halfway through the PUFA tail (at carbons 9‐12) are important for a high affinity interaction of PUFAs with Slo1 BK channels.…”