APLP2 (Amyloid Precursor-Like Protein 2), encoded by the APLP2 gene on chromosome 15q21.3, is a type-I transmembrane glycoprotein and the second of two known mammalian APP homologs (alongside APP and APLP1)[1]. Like APP and APLP1, APLP2 contains a large extracellular region with the characteristic E1 and E2 protein interaction domains, a single transmembrane helix, and a short cytoplasmic tail containing an YENPTY motif that recruits adaptor proteins controlling endocytosis and trafficking. Unlike APP, APLP2 does not produce amyloid-beta (Abeta) peptide — the proteolytic cleavage sites that generate Abeta from APP are not conserved in APLP2.
APLP2 is broadly expressed throughout the central nervous system and peripheral nervous system, with particularly high levels in neurons of the cerebral cortex, hippocampus, and cerebellum[1:1]. It plays essential roles in synaptic organization, trans-synaptic adhesion, neuronal excitability, and synaptic plasticity[2][3]. Critically, APLP2 is not merely a redundant paralog of APP — it has non-overlapping and partially compensated functions that make it essential for life when all APP family members are disrupted, yet redundant with APP in specific synaptic contexts[4]. Its relevance to Alzheimer's disease stems from the complex interplay within the APP family: therapies targeting APP processing inevitably affect APLP2 biology, and APLP2 compensation for APP deficiency shapes disease phenotypes and therapeutic responses[1:2][5].
| Property | Value |
|---|---|
| Gene Symbol | APLP2 |
| Protein Alias | APLP2, amyloid precursor-like protein 2 |
| Chromosomal Location | 15q21.3 |
| UniProt ID | Q06481 |
| Molecular Weight | ~87 kDa (mature, after N-glycosylation) |
| Amino Acids | 723 |
| Subcellular Localization | Plasma membrane, synaptic vesicles, endosomes, Golgi |
| Protein Family | APP protein family (APP, APLP1, APLP2) |
| Abeta Production | None (lacks Abeta sequence) |
APLP2 adopts the characteristic type-I transmembrane architecture shared by the APP family[1:3]:
APLP2 undergoes proteolytic processing similar to APP: alpha-secretase (ADAM10) cleaves within the A-beta sequence region (or its APLP2 equivalent), generating sAPLP2 (soluble ectodomain) and a C-terminal fragment (C83/alpha-CTF). Beta-secretase (BACE1) cleavage of APLP2 also occurs, generating sAPLP2-beta and C89/beta-CTF. Gamma-secretase then cleaves the CTF fragments to release AICD (APP intracellular domain), which translocates to the nucleus and may regulate gene transcription.
APLP2 functions as a synaptic adhesion molecule, forming trans-synaptic complexes that organize the presynaptic and postsynaptic apparatus[3:1][6]:
APLP2 regulates both basal synaptic transmission and activity-dependent plasticity[7][3:2]:
APLP2 modulates neuronal excitability through multiple mechanisms[2:1]:
APLP2 localizes to synaptic vesicles and regulates vesicle trafficking and release[7:1]:
APLP2 intersects with Alzheimer's disease through multiple mechanisms[1:4][5:1][8]:
APP family compensation: APLP2 frequently compensates for APP deficiency, which complicates interpretation of APP-targeted therapies:
Therapeutic implications of APP family biology:
APLP2 and lipid metabolism: APLP2 interacts with APOE receptors (LDLR family) and influences lipid metabolism[8:1]:
Stress response: APLP2 sumoylation plays a role in the neuronal stress response[9]:
APLP2 may also be relevant in other neurodegenerative conditions:
| Protein | Interaction Type | Functional Effect |
|---|---|---|
| APP | Heterophilic binding (E1/E2) | Trans-synaptic adhesion, functional redundancy |
| APLP1 | Heterophilic binding (E1/E2) | Synaptic scaffold formation |
| Fe65 (APBB1) | Tail interaction (YENPTY) | Transcriptional regulation via AICD |
| X11 alpha (APBA1) | Tail interaction | Regulates trafficking and processing |
| MUNC18 (STXBP1) | Tail interaction | Synaptic vesicle trafficking |
| Heparan sulfate proteoglycans | E2 domain binding | Cell surface retention, adhesion |
| Copper ions | E1 domain (CuBD) | Metal ion homeostasis |
| Zn2+ ions | E2 domain binding | Structural stabilization, adhesion |
| APOE | Receptor-mediated | Lipid metabolism and transport |
| LDLR family | Receptor interactions | Endocytosis and signaling |
APLP2 is not a primary drug target for neurodegeneration, but understanding its biology is essential for[1:5][5:3]:
Müller UC, Deller T, Korte M. Not just amyloid: physiological functions of the amyloid precursor protein family. Nature Reviews Neuroscience. 2017. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Lee SH, Kang J, Ho A, et al. APP Family Regulates Neuronal Excitability and Synaptic Plasticity but Not Neuronal Survival. Neuron. 2020. ↩︎ ↩︎
Weyer SW, Klevanski M, Delekate A, et al. APP and APLP2 are essential at PNS and CNS synapses for transmission, spatial learning and LTP. EMBO Journal. 2011. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
von Koch CS, Zheng H, Chen H, et al. Mice with combined gene knock-outs reveal essential and partially redundant functions of amyloid precursor protein family members. Journal of Neuroscience. 1997. ↩︎ ↩︎ ↩︎
Chen Y, et al. APLP2 and APP co-regulate synaptic homeostasis and network stability. Journal of Neuroscience. 2020. ↩︎ ↩︎ ↩︎ ↩︎ ↩︎
Troy CM, et al. APLP2 in axonal development and maintenance. Cellular and Molecular Life Sciences. 2012. ↩︎
Hoey SE, et al. APLP2 regulates synaptic vesicle cycling and neurotransmitter release. Journal of Neuroscience. 2009. ↩︎ ↩︎
Suh J, et al. APLP2 and APOE receptor interactions in lipid metabolism and neurodegeneration. Science Advances. 2020. ↩︎ ↩︎
Yuan H, et al. APLP2 sumoylation and its role in neuronal stress response and synaptic integrity. Proceedings of the National Academy of Sciences. 2022. ↩︎
Shariati SAM, Knaus P, Rezaei-Ghaleh N, et al. Deletion of the amyloid precursor-like protein 2 (APLP2) does not affect hippocampal neuron morphology or function. Neurobiology of Aging. 2012. ↩︎