The Effects of Transmembrane Sequence and Dimerization on Cleavage of the p75 Neurotrophin Receptor by γ-Secretase

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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.

Section: Pc12 Cells Exhibit An Enhancedsupporting

confidence: 80%

Section: Discussionmentioning

confidence: 99%

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An Intracellular Domain Fragment of the p75 Neurotrophin Receptor (p75NTR) Enhances Tropomyosin Receptor Kinase A (TrkA) Receptor Function

Matusica

Skeldal

Sykes

et al. 2013

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“…In addition, the TM domain of p75 self-associates as measured by ToxCAT (8). All these data are supported by FRET (8,9) and by ␤-galactosidase protein-protein interaction assays (19), indicating that in the absence of NTs a significant fraction of p75 exists as preformed dimers on the plasma membrane.Like several single span transmembrane receptors (20) p75 dimerization is not enough for its activation, and only specific disulfide-linked dimers, mediated by Cys 257 in the TM domain, respond to NGF binding (8). Although the p75-C257A mutant is still capable to form dimers and bind to NGF (8), it is unable to transduce the signals triggered by NGF binding in some cell signaling paradigms (8).…”

supporting

confidence: 54%

Structural Basis of p75 Transmembrane Domain Dimerization

Nadezhdin

Goncharuk

Mineev

et al. 2016

Dimerization of single span transmembrane receptors underlies their mechanism of activation. p75 neurotrophin receptor plays an important role in the nervous system, but the understanding of p75 activation mechanism is still incomplete. The transmembrane (TM) domain of p75 stabilizes the receptor dimers through a disulfide bond, essential for the NGF signaling. Here we solved by NMR the three-dimensional structure of the p75-TM-WT and the functionally inactive p75-TM-C257A dimers. Upon reconstitution in lipid micelles, p75-TM-WT forms the disulfide-linked dimers spontaneously. Under reducing conditions, p75-TM-WT is in a monomer-dimer equilibrium with the Cys 257 residue located on the dimer interface. In contrast, p75-TM-C257A forms dimers through the AXXXG motif on the opposite face of the ␣-helix. Biochemical and crosslinking experiments indicate that AXXXG motif is not on the dimer interface of p75-TM-WT, suggesting that the conformation of p75-TM-C257A may be not functionally relevant. However, rather than mediating p75 homodimerization, mutagenesis of the AXXXG motif reveals its functional role in the regulated intramembrane proteolysis of p75 catalyzed by the ␥-secretase complex. Our structural data provide an insight into the key role of the Cys 257 in stabilization of the weak transmembrane dimer in a conformation required for the NGF signaling.The neurotrophins (NTs) 6 are a family of neurotrophic factors that control multiple aspects of nervous system development and function. NTs interact with two distinct receptors, a cognate member of the Trk receptor tyrosine kinase family and the p75 neurotrophin receptor, a member of the tumor necrosis factor (TNF) receptor superfamily of death receptors (1). The most prominent biological function of p75 may be the induction of cell death, although it demonstrates several other activities, like survival, axonal growth, and cell migration (2-5).The precise mechanism as to how p75 transmits diverse signals in the normal or diseased nervous system remains elusive (3). Signal transduction by p75 is thought to proceed via the ligand-dependent recruitment and release of protein interactors to and from the receptor (6). Although different oligomer species have been recently described as the active receptor (7-10), several lines of evidence support the dimeric nature of p75 in neurotrophin signaling. NTs are homodimers in solution (11) that dimerize the extracellular domain of p75 upon binding as seen by in vivo cross-linking (12), by x-ray crystallography (13,14), and in solution (15). Engineered cysteine constructs activate p75 in the absence of NGF by inducing constitutive dimers (7), and the extracellular (16) and the intracellular domain (17, 18) form stable dimers in solution. In addition, the TM domain of p75 self-associates as measured by ToxCAT (8). All these data are supported by FRET (8,9) and by ␤-galactosidase protein-protein interaction assays (19), indicating that in the absence of NTs a significant fraction of p75 exists as preformed dimers on the plas...

“…FRET was calculated on cells as a FRET ratio, which is the fractional increase in YFP emission caused by FRET (26) according to the formula described in Ref. 34.…”

Section: Methodsmentioning

confidence: 99%

Mapping of the Interaction Site between Sortilin and the p75 Neurotrophin Receptor Reveals a Regulatory Role for the Sortilin Intracellular Domain in p75 Neurotrophin Receptor Shedding and Apoptosis

Skeldal

Sykes

Glerup

et al. 2012

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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 .