Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
Annotation inferences using phylogenetic trees
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara
The SALM family of adhesion-like molecules forms heteromeric and homomeric complexes.
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In rat brain and heterologous-cell experiments, SALM5 lacked the robust SALM1-3 brain heteromerization pattern and mediated homophilic, but not heterophilic, trans-cellular adhesion.
"Both SALMs 4 and 5 formed homophilic, but not heterophilic associations, whereas no trans associations were formed by the other SALMs."
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SALM5 lacks the C-terminal PDZ-binding domain present in SALM1-3.
"SALMs 1-3 contain PDZ-binding domains, whereas SALMs 4 and 5 do not."
Synaptic adhesion-like molecules (SALMs) promote neurite outgrowth.
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In cultured hippocampal neurons, overexpression of each SALM, including SALM5, enhanced neurite outgrowth, while extracellular-LRR antibodies and RNAi reduced it.
"Over-expression of each SALM resulted in enhanced neurite outgrowth, but with different phenotypes. Neurite outgrowth could be reduced by applying antibodies targeting the extracellular leucine rich regions of SALMs and with RNAi."
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Epitope-tagged SALM family proteins localized throughout axons, dendrites, and growth cones in cultured hippocampal neurons.
"Expression of epitope-tagged proteins in cultured hippocampal neurons showed that SALMs are distributed throughout neurons, including axons, dendrites, and growth cones."
Selected SALM (synaptic adhesion-like molecule) family proteins regulate synapse formation.
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SALM5, together with SALM3, induces both excitatory and inhibitory presynaptic differentiation in contacting axons.
"We found that expression of the SALM family proteins SALM3 and SALM5 in nonneural and neural cells induces both excitatory and inhibitory presynaptic differentiation in contacting axons."
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SALM5 is enriched in synaptic fractions, but unlike SALM3, aggregated SALM5 does not cluster PSD-95 on dendritic surfaces.
"SALM3 and SALM5 proteins are enriched in synaptic fractions, and form strong (SALM3) or weak (SALM5) complexes with postsynaptic density-95 (PSD-95), an abundant postsynaptic scaffolding protein at excitatory synapses. Aggregation of SALM3, but not SALM5, on dendritic surfaces induces clustering of PSD-95."
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SALM5 knockdown reduces both the number and function of excitatory and inhibitory synapses in cultured rat hippocampal neurons.
"Knockdown of SALM5 reduces the number and function of excitatory and inhibitory synapses."
Neuron-specific SALM5 limits inflammation in the CNS via its interaction with HVEM.
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Human and mouse SALM5 specifically bind HVEM/TNFRSF14; human HVEM did not detectably bind the other four human SALM family members in the reciprocal screen.
"The HVEM-Ig screening did not generate any positive signal in the wells containing the other four SALM family members, though members of the SALM family share about 50% homology in their protein sequences."
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The SALM5 LRR domain is sufficient for HVEM binding, whereas swapping its Ig or FN domain with SALM3 does not abolish binding.
"The LRR domain, but not the Ig or FN domain from SALM5, is sufficient to endow the binding capacity to HVEM"
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Cell-surface SALM5 suppresses LPS-induced macrophage activation, and blocking endogenous SALM5-HVEM signaling aggravates inflammation in mouse CNS models.
"As shown in Fig. 2C, the production of both IL-6 and TNFα from the cultured macrophages was significantly inhibited by SALM5+ HEK293T cells. Therefore, SALM5 directly suppressed macrophage activation, likely by engaging a putative receptor on macrophages."
SALM5 trans-synaptically interacts with LAR-RPTPs in a splicing-dependent manner to regulate synapse development.
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Mouse SALM5 binds all three LAR-family receptor phosphatases, and the SALM5 LRR-containing ectodomain engages their Ig domains.
"We found that SALM5-expressing cells coaggregated with cells expressing all three LAR-RPTPs (LAR, PTPδ, and PTPσ)."
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In cell-aggregation assays, mini-exon B strongly inhibited SALM5 binding to LAR, PTPδ, and PTPσ; the study used mouse full-length SALM5 and mixed human/mouse LAR-RPTP constructs.
"Taken together, these results suggest that the meA and meB splice inserts in LAR-RPTPs differentially regulate SALM5 binding, and that the meB splice insert strongly inhibits the SALM5–LAR-RPTP interactions."
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Loss of SALM5-LAR-RPTP binding abolishes presynaptic induction and prevents rescue of AMPA-receptor-mediated transmission after SALM5 knockdown in rat hippocampal preparations.
"When a mutant SALM5 (S329/S360A) that lacks LAR binding was used in the rescue experiment, it failed to rescue EPSCAMPA (Fig. 6c)."
Structural basis of trans-synaptic interactions between PTPδ and SALMs for inducing synapse formation.
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A human SALM5 LRR-Ig fragment and mouse PTPδ ectodomain fragment form a 2:2 structural complex in which an SALM5 dimer bridges two PTPδ molecules.
"We determined the crystal structures of apo-SALM5 (LRR–Ig), and PTPδ (Ig1–Ig3)–SALM2 (LRR–Ig) and PTPδ (Ig1–Fn1)–SALM5 (LRR–Ig) complexes at 3.08, 3.16, and 4.18 Å resolutions, respectively (Fig. 1 and Table 1)."
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Disrupting human SALM5 dimerization while retaining PTPδ binding strongly reduces presynapse-inducing activity, showing that dimerization is functionally required.
"Our synaptogenic co-culture assay using site-directed SALM5 mutants demonstrates that presynaptic differentiation induced by PTPδ-SALM5 requires the dimeric property of SALM5."
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Purified-protein SPR favored the PTPδ mini-exon-B-positive isoform, in contrast to the earlier cell-aggregation study.
"A9B– had a much lower (14%) affinity than A9B+ (Table 2 and Supplementary Fig. 2). The meB insertion likely plays an important role in placing PTPδ Ig3 at the position favorable for the interaction with SALM5 Ig."
Structural basis of SALM5-induced PTPδ dimerization for synaptic differentiation.
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Human SALM5 LRR-Ig forms an antiparallel dimer that bridges two human PTPδ Ig1-3 molecules in a 2:2 heterotetrameric complex.
"For the SALM5/PTPδ complex crystal, the asymmetric unit contained one dimeric complex, in a 2:2 stoichiometry, where a central SALM5 dimer bridges two monomeric PTPδ molecules together."
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A dimer-disrupting human SALM5 mutation retains PTPδ binding but abolishes SALM5-induced synapsin-I clustering in a rat-neuron heterologous synapse assay.
"This meant that R110N/E160S mutation abrogated the capacity of SALM5 to induce presynaptic differentiation. Taken together, disrupting SALM5 dimerization may significantly impair its functionality in mediating presynaptic differentiation."
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SPR with human fragments found that PTPδ mini-exon B enhances SALM5 binding by roughly 20- to 27-fold, conflicting with the earlier cell-aggregation result.
"In order to quantitatively evaluate how the splice inserts in PTPδ affect SALM5 binding, we carried out SPR experiments (Fig. 5), which clearly showed that the addition of MeB to PTPδ significantly enhanced PTPδ/SALM5 interaction (by 27 or 20 folds, respectively, for the presence or absence of MeA)."
A Human IgSF Cell-Surface Interactome Reveals a Complex Network of Protein-Protein Interactions.
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A human extracellular-domain interactome independently confirmed that human SALM5 binds each LAR-family receptor phosphatase, PTPRF, PTPRD, and PTPRS.
"With the exception of PTPRF-SALM4, we observed binding of all LAR-PTPRs to all SALMs"
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The three human LAR-RPTP-SALM5 pairs were previously known interactions and were all validated by SPR in the study.
"SALM5PTPRDknownN/APTPRFknownN/APTPRSknownN/A"