LRRC52

LRRC52 is an auxiliary γ subunit of large-conductance potassium channels that tunes channel voltage dependence in sperm and cochlear inner hair cells. It physically associates with SLO3 (KSper) in sperm, shifting channel gating into the physiological voltage and pH range required for normal potassium conductance, membrane potential regulation, flagellar pH homeostasis, calcium signaling, motility, and the acrosome reaction; genetic ablation of LRRC52 in mice causes severely impaired male fertility (PMID:22084117, PMID:25675513, PMID:38267364, PMID:39498893). In cochlear inner hair cells, LRRC52 is the dominant γ subunit for BK (SLO1) channels, where it colocalizes with BKα at the cell neck, is required for BK channel clustering, and produces a large hyperpolarizing shift in activation voltage that, together with specific BK splice variants and mechanical force, enables calcium-independent BK activation at negative potentials (PMID:31451634, PMID:31348683, PMID:39515584). LRRC52 protein stability depends on its pore-forming partner (SLO3 or BKα), its extracellular leucine-rich repeat domain requires N-glycosylation for proper expression and channel modulation, and the SLO3/LRRC52 complex remains subject to phosphoinositide regulation (PMID:35104503, PMID:34980136, PMID:32564653).

1. 2011 High

   Establishing that LRRC52 is a physical partner and functional modifier of SLO3 resolved the long-standing discrepancy between recombinant SLO3 currents and native KSper gating properties in sperm.

   Evidence Co-immunoprecipitation, heterologous co-expression electrophysiology, and Slo3 knockout mouse sperm analysis

   PMID:22084117

   Open questions at the time

   • Stoichiometry of the SLO3–LRRC52 complex unknown
   • Structural basis of the gating shift unresolved
   • Whether other auxiliary subunits contribute to native KSper not addressed
2. 2012 High

   Demonstrating that LRRC52 also produces a ~100 mV negative shift in BK (SLO1) channel activation in the absence of calcium established it as a general γ-type auxiliary subunit for the SLO channel family, not restricted to SLO3.

   Evidence Heterologous co-expression of LRRC52 with BKα and whole-cell patch clamp in two independent studies, including human SLO3

   PMID:22547800 PMID:23129643

   Open questions at the time

   • Whether LRRC52 modulates SLO1 in a native tissue not yet shown at this point
   • Molecular determinants of LRRC52–channel interaction uncharacterized
3. 2015 High

   The LRRC52 knockout mouse proved that LRRC52 is essential for setting native KSper gating properties in vivo and is required for male fertility, moving LRRC52 from a candidate auxiliary subunit to a physiologically necessary one.

   Evidence LRRC52 knockout mouse with whole-cell sperm electrophysiology and in vitro fertilization assays

   PMID:25675513

   Open questions at the time

   • Specific step of fertilization failure (capacitation, zona binding, fusion) not dissected
   • Compensatory changes in other γ subunits not evaluated
4. 2019 High

   Identification of LRRC52 as the dominant BK channel γ subunit in cochlear inner hair cells — rather than LRRC26 — and the finding that its loss disrupts BK channel clustering revealed a second critical physiological role for LRRC52 and an unexpected function in channel localization.

   Evidence LRRC52 and LRRC26 knockout mice with IHC patch clamp electrophysiology, immunohistochemistry, and proximity ligation assay demonstrating <40 nm colocalization with BKα

   PMID:31348683 PMID:31451634

   Open questions at the time

   • Mechanism by which LRRC52 promotes BK channel clustering unknown
   • Whether LRRC52 loss affects hearing function not directly tested
   • Whether LRRC52 stability depends on BKα in IHCs only correlatively shown via BKα and Cav1.3 KOs
5. 2020 Medium

   Showing that PtdIns(4,5)P2 depletion suppresses SLO3 activity even with LRRC52 present demonstrated that LRRC52 does not override lipid-based regulation, adding phosphoinositide sensitivity as a layer of control over the complex.

   Evidence Voltage-sensing phosphatase co-expression with SLO3/LRRC52 in Xenopus oocytes and electrophysiology

   PMID:32564653

   Open questions at the time

   • Whether phosphoinositide regulation is direct on SLO3, LRRC52, or both is unclear
   • Physiological relevance in sperm membrane not tested
   • Single heterologous system, single lab
6. 2022 High

   Determining that the LRRC52 LRR domain is extracellular and that N-glycosylation is required for its expression and BK modulation provided the first topological and post-translational insight into how LRRC52 reaches and modulates its channel partners.

   Evidence Cell surface immunoprecipitation, N-glycosylation site mutants, enzymatic deglycosylation, and electrophysiology

   PMID:35104503

   Open questions at the time

   • Specific glycosylation sites critical for function not fully mapped
   • No high-resolution structure of LRRC52 alone or in complex with a channel
   • Whether glycosylation affects trafficking versus stability versus channel interaction not distinguished
7. 2022 Medium

   A human SLO3 missense mutation reducing LRRC52 protein levels in patient sperm confirmed that the SLO3-dependent stabilization of LRRC52 observed in mouse knockout studies is conserved in humans.

   Evidence Whole-exome sequencing, western blot, and immunofluorescence in patient spermatozoa carrying homozygous SLO3 c.1237A>T

   PMID:34980136

   Open questions at the time

   • Single patient family; broader prevalence of SLO3 mutations affecting LRRC52 unknown
   • Whether LRRC52 loss alone explains the human infertility phenotype not separated from SLO3 dysfunction
8. 2024 High

   Direct demonstration that an antibody against the LRRC52 extracellular domain inhibits human KSper, depolarizes sperm, impairs Ca2+ signaling, motility, and acrosome reaction established LRRC52 as a functional and accessible component of the human KSper complex and linked it to flagellar pH homeostasis.

   Evidence Polyclonal antibody inhibition of human sperm with patch clamp, Ca2+ imaging, motility and acrosome reaction assays, and single-cell pH recording

   PMID:38267364 PMID:39498893

   Open questions at the time

   • Antibody specificity controls limited to peptide competition; genetic validation in human cells not performed
   • Mechanism of pH coupling (direct versus indirect via membrane potential) not fully resolved
9. 2024 Medium

   Reconstitution of BK splice variants (STREX2, alt9) with LRRC52 showed additive negative voltage shifts, explaining how Ca2+-independent BK activation at resting potentials is achieved in IHCs through combinatorial subunit and splicing mechanisms.

   Evidence Heterologous expression of defined BK isoforms with LRRC52, patch clamp electrophysiology, and mechanical stimulation

   PMID:39515584

   Open questions at the time

   • In vivo validation of splice-variant contributions in IHCs not performed
   • Whether mechanical sensitivity of BK in IHCs requires LRRC52 not tested
   • Single study, single lab

• No high-resolution structure of LRRC52 alone or in complex with SLO3/BKα exists, leaving the molecular basis of the gating shift, the interaction interface, and the mechanism by which LRRC52 promotes channel clustering unresolved.
• No cryo-EM or crystal structure of LRRC52 or its channel complexes
• Stoichiometry of γ subunit per channel tetramer undetermined
• Whether LRRC52 has functions independent of SLO-family channels unexplored