LRRC52

LRRC52 is a leucine-rich repeat-containing auxiliary subunit (the BK γ2 subunit) that associates with Slo-family potassium channels to drive large negative shifts in their voltage dependence of activation, thereby enabling channel opening at physiological membrane potentials (PMID:22084117, PMID:22547800). In testis, it associates with the sperm-specific SLO3 channel and shifts its gating to the voltages and pH characteristic of the native KSper current; its own expression is critically dependent on the presence of SLO3 (PMID:22084117, PMID:23129643). As a member of the γ family of BK auxiliary proteins—distinct from β subunits—LRRC52 produces a ~100 mV hyperpolarizing shift in the voltage dependence of SLO1/BK channel activation in the absence of calcium (PMID:22547800). Genetic ablation in mice establishes its physiological roles: LRRC52-null sperm require more positive voltages and higher pH for KSper activation, and the mice are severely subfertile (PMID:25675513); in cochlear inner hair cells, knockout shifts BK current activation by more than +200 mV and disrupts BK channel clustering, identifying LRRC52 as essential for Ca2+-independent BK activation at negative potentials and for correct channel localization (PMID:31451634, PMID:39515584). LRRC52 localizes within ≤40 nm of BKα in IHC necks and requires both BKα and Cav1.3 for its expression, consistent with assembly into a stable macromolecular channel complex (PMID:31348683). Antibody targeting of its extracellular segment inhibits native mouse and human KSper, depolarizing the sperm membrane, acidifying flagellar pH, and impairing motility and the acrosome reaction—defining KSper-dependent control of membrane potential and pH homeostasis as a requirement for human sperm function (PMID:38267364, PMID:39498893). Structurally, the LRR domain is extracellular and dispensable for maximal gating modulation, while N-glycosylation is required for full protein expression (PMID:35104503).

1. 2011 High

   Established LRRC52 as the long-sought auxiliary subunit that reconciles SLO3's heterologous gating with the native sperm KSper current, answering why SLO3 alone failed to recapitulate KSper.

   Evidence Heterologous co-expression with electrophysiology plus western blotting in Slo3 knockout mouse testis

   PMID:22084117

   Open questions at the time

   • Did not resolve the structural interface between LRRC52 and SLO3
   • Mechanism by which SLO3 controls LRRC52 protein stability not defined
2. 2012 High

   Defined LRRC52 as the BK channel γ2 subunit, showing it acts on SLO1/BK (not only SLO3) and classifying it within a distinct γ family of auxiliary proteins separate from β subunits.

   Evidence Heterologous expression in oocytes/HEK cells with electrophysiology, comparing LRRC paralogs

   PMID:22547800 PMID:23129643

   Open questions at the time

   • Native tissue context of BK modulation not yet established in 2012
   • Stoichiometry of LRRC52:channel assembly not determined
3. 2015 High

   Demonstrated through gene knockout that LRRC52 is physiologically required for normal KSper gating and male fertility, moving it from a heterologous modulator to an essential native component.

   Evidence LRRC52 knockout mouse with sperm patch-clamp electrophysiology and in vitro fertilization assays

   PMID:25675513

   Open questions at the time

   • Did not address non-testis roles of LRRC52
   • Downstream consequences for sperm pH or motility not directly measured
4. 2019 High

   Extended LRRC52 function to cochlear inner hair cells, revealing it is required both for Ca2+-independent BK gating at negative potentials and for correct BK channel clustering, implicating it in macromolecular complex assembly.

   Evidence LRRC52 knockout mouse with patch-clamp and confocal localization, plus proximity ligation assay and BKα/Cav1.3 knockout validation

   PMID:31348683 PMID:31451634

   Open questions at the time

   • Molecular basis for LRRC52-dependent channel clustering unresolved
   • How Cav1.3 controls LRRC52 expression not mechanistically defined
5. 2020 Medium

   Addressed whether LRRC52 alters lipid regulation of the channel, showing the Slo3/LRRC52 complex retains PtdIns(4,5)P2 sensitivity comparable to Slo3 alone.

   Evidence Heterologous oocyte expression with VSP-mediated phosphoinositide depletion and electrophysiology

   PMID:32564653

   Open questions at the time

   • Single-lab heterologous result not confirmed in native sperm
   • Did not map a phosphoinositide interaction site
6. 2022 Medium

   Defined the structural topology and biogenesis requirements of LRRC52, placing the LRR domain extracellularly, showing N-glycosylation is needed for full expression, and that the LRR domain is dispensable for maximal gating modulation.

   Evidence Cell-surface immunoprecipitation, N-glycosylation mutants and enzymatic blockade, molecular dynamics, western blot

   PMID:35104503

   Open questions at the time

   • Functional role of the extracellular LRR domain remains unexplained
   • Which transmembrane/intracellular segment mediates gating modulation not pinpointed
7. 2024 High

   Validated LRRC52 as a functional component of human KSper and linked KSper activity to sperm physiology, showing antibody blockade of its extracellular segment depolarizes membrane potential, acidifies flagellar pH, and impairs motility, Ca2+ signaling and the acrosome reaction.

   Evidence Co-immunoprecipitation, patch-clamp of mouse and human sperm, antibody (LID1) inhibition, single-cell pH and Ca2+ imaging, motility and acrosome assays, with high-K+ ionic rescue

   PMID:38267364 PMID:39498893

   Open questions at the time

   • Causal contribution of LRRC52 to human male infertility in patients not established
   • Whether LID1 acts directly on LRRC52 or sterically on the complex not fully resolved
8. 2024 Medium

   Reconstituted the determinants of Ca2+-independent BK activation in IHCs, showing LRRC52 acts together with IHC-specific BK splice isoforms and mechanical force additively to shift voltage dependence at zero calcium.

   Evidence Heterologous expression of LRRC52 with STREX/exon2+alt9 BK splice variants, patch-clamp, and IHC-specific BK conditional knockout for auditory phenotype

   PMID:39515584

   Open questions at the time

   • Relative in vivo contributions of LRRC52 versus splicing versus force not quantified
   • Single-lab reconstitution

• The structural interface of LRRC52 with SLO1/SLO3 and the mechanism by which it produces large voltage-dependence shifts and channel clustering remain undefined.
• No high-resolution structure of an LRRC52-channel complex in the corpus
• Assembly stoichiometry and the segment mediating gating modulation unmapped
• Role of LRRC52 in human disease/infertility genetics untested