LRTM1

Model summary

A single-pass cell-surface organizer that presents an extracellular leucine‑rich repeat scaffold to bind and cluster partner proteins at the plasma membrane. By stabilizing presynaptic assemblies and biasing membrane-associated processing pathways, it modulates synapse formation and can enhance amyloidogenic processing of precursor substrates. Its mechanism relies on a stabilized extracellular repeat array capped by a cysteine-rich module that anchors the complex and tunes endocytic and proteolytic pathways at neuronal membranes.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The N-terminal half is dominated by tandem leucine-rich repeat (LRR) modules: IPR032675 (Leucine-rich repeat domain superfamily, residues 17–138) followed by a second LRR superfamily block IPR032675 (residues 139–234), indicating an extended extracellular LRR solenoid. Within this scaffold sit multiple typical LRR repeats: IPR003591 repeat units at 53–72, 73–96, 97–120, 121–144, and 145–168, together with a core LRR annotation IPR001611 spanning 76–144. This array of repeats forms a curved β-sheet horseshoe that presents a high-affinity, shape-complementary binding surface. The architecture is capped by IPR000483 (Cysteine-rich flanking region, C-terminal, residues 180–233), a hallmark “LRRCT” module that stabilizes the terminal end of the LRR stack and often defines the boundary of an extracellular ectodomain in single-pass receptors. The family signature IPR050541 (Leucine-rich repeat and transmembrane domain-containing protein, residues 10–120) ties this LRR scaffold to a membrane-anchored configuration, consistent with a single-pass type I membrane protein whose N-terminal LRR ectodomain projects outside the cell.

2. 02

   This ordered LRR ectodomain followed by a cysteine-rich cap and a single transmembrane segment causes avid, selective protein binding at the cell surface rather than enzymatic catalysis.

   The repetitive LRR surface and the absence of catalytic motifs support GO:0005515 protein binding as the primary molecular function. The extracellular binding platform, tethered to the membrane by a single-pass helix, is ideally suited to capture or cluster partner proteins.

3. 03

   From this binding-centric mechanism, two higher-order processes follow.

   First, the LRR ectodomain can organize presynaptic assemblies by clustering adhesion molecules and signaling hubs at the neuronal surface, driving GO:1905606 regulation of presynapse assembly. The LRR scaffold’s multivalent avidity and membrane anchoring provide the physical basis for assembling presynaptic scaffolds and aligning vesicle release machinery. Second, by concentrating and modulating membrane-associated processing pathways, the same ectodomain can bias amyloidogenic processing—consistent with GO:1902004 positive regulation of amyloid-beta formation and GO:1902993 positive regulation of amyloid precursor protein catabolic process. A plausible route is that extracellular clustering of surface complexes alters endocytic trafficking and local protease access to amyloid precursor substrates.

4. 04

   The cellular context is dictated by the architecture and topology.

   The presence of an extensive extracellular LRR array capped by an LRRCT domain and a single-pass anchor places the protein at the cell surface, matching GO:0005886 plasma membrane and the experimentally supported single-pass type I membrane localization. This surface positioning enables it to sense and organize extracellular and juxtamembrane assemblies that feed into synaptic and amyloidogenic pathways.

5. 05

   Mechanistically, I hypothesize that the LRR ectodomain nucleates higher-order clusters of presynaptic organizers and amyloidogenic machinery.

   Likely partners include presynaptic adhesion and scaffold proteins (e.g., neurexins/neuroligins), membrane–cytoskeleton linkers (spectrin/ankyrin complexes), and endocytic adaptors that govern substrate trafficking. By stabilizing these assemblies at the plasma membrane, the protein modulates presynaptic assembly and increases the local efficiency of amyloid precursor processing toward amyloid-beta formation.