Crystal structure of the neurotrophin-3 and p75NTR symmetrical complex

Abstract

Neurotrophins (NTs) are important regulators for the survival, differentiation and maintenance of different peripheral and central neurons. NTs bind to two distinct classes of glycosylated receptor: the p75 neurotrophin receptor (p75(NTR)) and tyrosine kinase receptors (Trks). Whereas p75(NTR) binds to all NTs, the Trk subtypes are specific for each NT. The question of whether NTs stimulate p75(NTR) by inducing receptor homodimerization is still under debate. Here we report the 2.6-A resolution crystal structure of neurotrophin-3 (NT-3) complexed to the ectodomain of glycosylated p75(NTR). In contrast to the previously reported asymmetric complex structure, which contains a dimer of nerve growth factor (NGF) bound to a single ectodomain of deglycosylated p75(NTR) (ref. 3), we show that NT-3 forms a central homodimer around which two glycosylated p75(NTR) molecules bind symmetrically. Symmetrical binding occurs along the NT-3 interfaces, resulting in a 2:2 ligand-receptor cluster. A comparison of the symmetrical and asymmetric structures reveals significant differences in ligand-receptor interactions and p75(NTR) conformations. Biochemical experiments indicate that both NT-3 and NGF bind to p75(NTR) with 2:2 stoichiometry in solution, whereas the 2:1 complexes are the result of artificial deglycosylation. We therefore propose that the symmetrical 2:2 complex reflects a native state of p75(NTR) activation at the cell surface. These results provide a model for NTs-p75(NTR) recognition and signal generation, as well as insights into coordination between p75(NTR) and Trks.

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

“…NTR -TrkA heterodimer model is not supported by structural data (15)(16)(17), and the ligand passing model, although consistent with the finding that a NGF mutant that cannot bind p75 NTR has only low binding affinity (18), is inconsistent with the observation that the extracellular ligand-binding domain of p75 NTR is not required to create high-affinity NGF binding sites (19,20). Therefore, although a heteroreceptor complex may form, and ligand transfer from p75 NTR to TrkA could occur, these mechanisms cannot be the sole basis for the formation of high-affinity binding sites.…”

Assembly and activation of neurotrophic factor receptor complexes

“…Multimerization of neurotrophin receptors can appear at various levels: homomerization, heteromerization, and interaction with other membrane-associated proteins. Chemical cross-linking studies (Klein et al, 1991;Rydén et al, 1997)--beautifully confirmed by more recent high-resolution structural analyses (Wiesmann et al, 1999;Wehrman et al, 2007;Gong et al, 2008)--indicate that both Trk and p75 NTR receptors interact as homodimers with the mature form of neurotrophins [ Fig. 1(A,B)].…”

Neurotrophins and B-cell malignancies

“…Its structure, as determined independently by three groups, contains a cysteine-rich cytoplasmic domain, a single-pass transmembrane domain and an intracellular death domain [79][80][81]. It can signal in either monomeric or dimeric form upon ligand binding [82].…”