Trafficking defects in PAS domain mutant Kv11.1 channels: roles of reduced domain stability and altered domain–domain interactions

Abstract

Loss of Kv11.1 potassium channel function is the underlying cause of pathology in long-QT syndrome type 2, one of the commonest causes of sudden cardiac death in the young. Previous studies have identified the cytosolic PAS (Per/Arnt/Sim) domain as a hotspot for mutations that cause Kv11.1 trafficking defects. To investigate the underlying basis of this observation, we have quantified the effect of mutants on domain folding as well as interactions between the PAS domain and the remainder of the channel. Apart from R56Q, all mutants impaired the thermostability of the isolated PAS domain. Six mutants, located in the vicinity of a hydrophobic patch on the PAS domain surface, also affected binding of the isolated PAS domain to an N-terminal truncated hERG (human ether-a-go-go-related gene) channel. Conversely, four other surface mutants (C64Y, T65P, A78P and I96T) and one buried mutant (L86R) did not prevent the isolated PAS domain binding to the truncated channels. Our results highlight a critical role for interactions between the PAS domain and the remainder of the channel in the hERG assembly and that mutants that affect PAS domain interactions with the remainder of the channel have a more severe trafficking defect than that caused by domain unfolding alone.

Patients With Long-QT Syndrome Caused by Impaired hERG -Encoded K v 11.1 Potassium Channel Have Exaggerated Endocrine Pancreatic and Incretin Function Associated With Reactive Hypoglycemia

“…Severity analysis has identified the PAS domain of hERG as a region where mutations increase susceptibility to disease dramatically 37 by causing severe trafficking defects. 19 Serious incidences of hypoglycemia have previously been observed both in children with LQT2 33 and in LQT1. 7 Our demonstration that LQT2 patients, also in the absence of β-blockers, have increased risk of reactive hypoglycemia should lead to a greater awareness of the risk of glucose-induced hypoglycemia in LQTS.…”

“…17,18 The first 3 mutations mentioned are located in the Per-Arnt-Sim (PAS) domain, which contains a signal-sensing region and causes trafficking defects. 19 I400N is in the S1 transmembrane segment and disrupts the voltage-sensing unit. 17 G572R is in the S5 transmembrane segment and the pore-forming unit, and causes reduced activation of the channel or disturbs the channel’s gating properties.…”

The S1 helix critically regulates the finely tuned gating of Kv11.1 channels

“…These electrophysiological recordings were undertaken at room temperature, rather than at physiological temperature (37°C), which is known to slow gating kinetics (62). Even so, it is likely that the relative differences between WT and mutants will be similar in different expression systems, as shown previously for mutations F29L (14,18,63) and R56Q (14,(63)(64)(65).…”

hERG quality control and the long QT syndrome

“…; Ke et al . ). For many years, the hERG loss‐of‐expression phenotype was attributed to impaired biosynthetic maturation and plasma membrane (PM) insertion.…”

“…There is significant variation in the expression defect between mutations; some completely abolish expression of mature hERG while others exhibit a milder phenotype (Ke et al . ; Anderson et al . ).…”