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Background:The mechanism by which the p75 neurotrophin receptor (p75 NTR ) and TrkA interact to enhance neurotrophin signaling is unknown. Results: The p75NTR intracellular domain fragment, p75 ICD , but not full-length p75 NTR enhanced NGF binding to TrkA and neurite outgrowth. Conclusion:The results suggest that p75 ICD causes a conformational change within the extracellular domain of TrkA. Significance: The findings challenge our current understanding of how p75 NTR enhances neurotrophic activity.

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Background: Sortilin and p75NTR induce neuronal apoptosis by binding pro-neurotrophins during development and following neuronal injury. Results: Sortilin interacts with an extracellular juxtamembrane 23-amino acid sequence of p75 NTR . Conclusion: Despite binding being mediated through extracellular interactions, the intracellular domain of sortilin regulates p75 NTR shedding and apoptosis. Significance: Mapping may allow design of compounds inhibiting neuronal cell death by blocking the interaction between sortilin and p75 NTR .

Copper-transporting P(IB)-type ATPases are highly conserved, and while unicellular eukaryotes and invertebrates have only one, a gene duplication has occurred during vertebrate evolution. Copper-induced trafficking of mammalian ATP7A and ATP7B from the trans-Golgi Network towards the plasma membrane is critical for their role in copper homeostasis. In polarized epithelial cells ATP7A and ATP7B traffic towards the basolateral and apical membranes respectively. We examined the localization and function of DmATP7, the single Drosophila melanogaster orthologue, in cultured D. melanogaster and mammalian cells to explore the conservation of P(IB)-type ATPase function. Comparative genomic analysis demonstrated motifs involved in basolateral targeting and retention of ATP7A were conserved in DmATP7, whereas ATP7B targeting motifs were not. DmATP7 expression was able to correct the copper hyper-accumulation phenotype of cultured fibroblasts from a Menkes disease patient expressing a null ATP7A allele. DmATP7 was able to transport copper to the cupro-enzyme tyrosinase and under elevated copper conditions DmATP7 was able to traffic towards the plasma membrane and efflux copper, essentially phenocopying ATP7A. When expressed in polarized Madin-Darby Canine Kidney cells, DmATP7 translocated towards the basolateral membrane when exposed to elevated copper, similar to ATP7A. These results demonstrate DmATP7 is able to functionally compensate for the absence of ATP7A, with important trafficking motifs conserved in these distantly related orthologues.