ATP11B

ATP11B Full Name

ATPase, class VI, type 11B

ATP11B Introduction

ATP11B (also known as ATPase class VI type 11B) is a member of the P4-ATPase subfamily of phospholipid flippases, which are transmembrane proteins that actively transport aminophospholipids such as phosphatidylserine (PS) and phosphatidylethanolamine (PE) from the outer leaflet to the inner leaflet of cellular membranes. This asymmetric distribution of phospholipids is essential for numerous cellular processes including membrane curvature, vesicle formation, cell signaling, blood coagulation, and apoptosis. ATP11B is ubiquitously expressed with particularly high levels in the brain, testis, and kidney, and localizes primarily to the recycling endosomes and the trans-Golgi network. Unlike the well-characterized ATP8A1 and ATP8B1, ATP11B remains relatively understudied, but emerging evidence implicates it in neurological function, cancer progression, and the cellular response to stress. ATP11B functions as a flippase in complex with its obligatory subunit TMEM30A (CDC50A), which is required for proper folding, trafficking, and catalytic activity of the ATPase. Dysregulation of ATP11B expression or function has been linked to autism spectrum disorder (ASD), intellectual disability, and various cancers, positioning ATP11B as an increasingly recognized player in both neurodevelopment and tumor biology.

Figure 1. Schematic structure of ATP11B.

Gene Structure and Protein Architecture
The human ATP11B gene is located on chromosome 3q26.33 and spans approximately 120 kb, containing 29 exons. Alternative splicing generates multiple transcript variants, with the major isoform encoding a protein of 1,256 amino acids with a calculated molecular weight of approximately 140 kDa. ATP11B contains several structurally and functionally important domains characteristic of P4-ATPases. The N-terminal region contains a calmodulin-binding domain that mediates calcium-dependent regulation of flippase activity. Following the calmodulin-binding domain, ATP11B contains two large cytoplasmic loops (the actuator domain and the phosphorylation domain) that constitute the catalytic core of the ATPase. The actuator domain contains the highly conserved DGET (Asp-Gly-Glu-Thr) motif, and the phosphorylation domain contains the conserved DKTGT (Asp-Lys-Thr-Gly-Thr) motif that forms the aspartyl-phosphate intermediate during the catalytic cycle. The C-terminal region contains eight transmembrane helices that form the channel through which phospholipids are translocated. Key residues within these helices, particularly conserved glycine, proline, and tyrosine residues, are critical for substrate recognition and transport. ATP11B also contains an N-terminal P-type ATPase signature sequence and multiple phosphorylation sites that regulate its activity and membrane localization. The obligatory subunit TMEM30A (CDC50A) interacts with the transmembrane domains of ATP11B, stabilizing the complex and facilitating its trafficking from the endoplasmic reticulum to the Golgi and endosomal compartments.

Regulation, Interacting Partners, and Therapeutic Implications
The expression and activity of ATP11B are tightly regulated at multiple levels. Transcriptionally, ATP11B is regulated by the transcription factor SP1 and by the tumor suppressor p53. Under conditions of cellular stress, p53 represses ATP11B expression, promoting PS externalization and facilitating apoptosis. This p53-dependent repression may contribute to the tumor suppressor functions of p53 by preventing pro-survival flippase activity in stressed cells. Post-translationally, ATP11B activity is regulated by calcium via its calmodulin-binding domain; elevated calcium enhances flippase activity, linking phospholipid transport to calcium signaling. ATP11B also undergoes phosphorylation by protein kinase A (PKA) and PKC, which modulate its activity and membrane localization. The obligatory subunit TMEM30A is critical for ATP11B function; TMEM30A knockdown phenocopies ATP11B loss, disrupting endosomal trafficking and increasing PS exposure. Additionally, ATP11B interacts with the small GTPase Rab11, which targets the ATP11B-TMEM30A complex to recycling endosomes, and loss of Rab11 function mislocalizes ATP11B to the plasma membrane. Therapeutically, ATP11B has emerged as a potential target for cancer treatment, particularly in glioblastoma and breast cancer. Small molecule inhibitors of P4-ATPases, including compounds that target the ATP-binding site or disrupt the TMEM30A interaction, are in preclinical development. The antifungal drug lovastatin has been reported to inhibit ATP11B activity, and lovastatin treatment phenocopies ATP11B knockdown in cancer cells, reducing cell proliferation and inducing apoptosis. However, the specificity of lovastatin for ATP11B versus other P4-ATPases is not yet established. In neurodevelopmental disorders, strategies to enhance ATP11B expression or activity are being explored, though delivering agents across the blood-brain barrier remains a significant challenge. Additionally, ATP11B expression levels or genetic variants may serve as biomarkers for ASD risk, cognitive outcomes, or cancer prognosis, though further validation in large cohorts is needed.

Alternate Names for ATP11B

ATP11B; ATPase, class VI, type 11B; ATPase, Class VI, type 11B; probable phospholipid-transporting ATPase IF; ATPIF; ATPIR; KIAA0956; ATPase IR; MGC46576; DKFZp434J238; DKFZp434N1615;