title: The effects of transmembrane sequence and dimerization on cleavage of the p75 neurotrophin receptor by γ-secretase.
abstract: Cleavage of transmembrane receptors by γ-secretase is the final step in the process of regulated intramembrane proteolysis (RIP) and has a significant impact on receptor function. Although relatively little is known about the molecular mechanism of γ-secretase enzymatic activity, it is becoming clear that substrate dimerization and/or the α-helical structure of the substrate can regulate the site and rate of γ-secretase activity. Here we show that the transmembrane domain of the pan-neurotrophin receptor p75(NTR), best known for regulating neuronal death, is sufficient for its homodimerization. Although the p75(NTR) ligands NGF and pro-NGF do not induce homerdimerization or RIP, homodimers of p75(NTR) are γ-secretase substrates. However, dimerization is not a requirement for p75(NTR) cleavage, suggesting that γ-secretase has the ability to recognize and cleave each receptor molecule independently. The transmembrane cysteine 257, which mediates covalent p75(NTR) interactions, is not crucial for homodimerization, but this residue is required for normal rates of γ-secretase cleavage. Similarly, mutation of the residues alanine 262 and glycine 266 of an AXXXG dimerization motif flanking the γ-secretase cleavage site within the p75(NTR) transmembrane domain alters the orientation of the domain and inhibits γ-secretase cleavage of p75(NTR). Nonetheless, heteromer interactions of p75(NTR) with TrkA increase full-length p75(NTR) homodimerization, which in turn potentiates the rate of γ-cleavage following TrkA activation independently of rates of α-cleavage. These results provide support for the idea that the helical structure of the p75(NTR) transmembrane domain, which may be affected by co-receptor interactions, is a key element in γ-secretase-catalyzed cleavage.
authors.affiliation: Queensland Brain Institute, University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Alex M
authors.initials: AM
authors.lastname: Sykes
authors.forename: Nickless
authors.initials: N
authors.lastname: Palstra
authors.forename: Daniel
authors.initials: D
authors.lastname: Abankwa
authors.forename: Justine M
authors.initials: JM
authors.lastname: Hill
authors.forename: Sune
authors.initials: S
authors.lastname: Skeldal
authors.forename: Dusan
authors.initials: D
authors.lastname: Matusica
authors.forename: Prahatha
authors.initials: P
authors.lastname: Venkatraman
authors.forename: John F
authors.initials: JF
authors.lastname: Hancock
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Coulson
mesh_terms: D020816:Amino Acid Motifs; D053829:Amyloid Precursor Protein Secretases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016923:Cell Death / Q000502:physiology; D003545:Cysteine; D004789:Enzyme Activation; D057809:HEK293 Cells; D006801:Humans; D020932:Nerve Growth Factor / Q000235:genetics / Q000378:metabolism; D009414:Nerve Growth Factors / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D016716:PC12 Cells; D055503:Protein Multimerization / Q000502:physiology*; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D051381:Rats; D020917:Receptor, trkA / Q000235:genetics / Q000378:metabolism; D017978:Receptors, Growth Factor / Q000235:genetics / Q000378:metabolism*; D017475:Receptors, Nerve Growth Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: C484065:NGFR protein, human; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D011498:Protein Precursors; D017978:Receptors, Growth Factor; D017475:Receptors, Nerve Growth Factor; C061397:pro-nerve growth factor, human; C514218:pro-nerve growth factor, rat; C068313:Ngfr protein, rat; D020932:Nerve Growth Factor; D020917:Receptor, trkA; D053829:Amyloid Precursor Protein Secretases; D003545:Cysteine