Rydén M, Ibáñez C F
Laboratory of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institute, 171 77 Stockholm, Sweden.
J Biol Chem. 1996 Mar 8;271(10):5623-7. doi: 10.1074/jbc.271.10.5623.
Neurotrophins regulate differentiation and survival of vertebrate neurons through binding to members of the Trk family of receptor tyrosine kinases and to a common low affinity receptor, p75LNGFR. The specificity of neurotrophin action is determined by their selective interaction with the different members of the Trk family; TrkA, TrkB, and TrkC serve as cognate receptors for nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 (NT-3), respectively. Unlike nerve growth factor and brain-derived neurotrophic factor, NT-3 can to some extent also bind and activate non-cognate TrkA and B receptors, although the physiological relevance of these interactions is unclear. Previous studies established that neurotrophins use an extended surface for binding to cognate Trk receptors, while binding to p75LNGFR is mediated by a localized cluster of positively charged residues. Here we show that the binding site of NT-3 to its non-preferred receptors TrkA and TrkB is dominated by two positively charged residues, Arg-31 and His-33, previously shown to constitute a main determinant of binding to p75LNGFR. Simultaneous mutation of these two residues into Ala completely abolished NT-3 binding and signaling through TrkA and greatly diminished binding and activation of TrkB. However, NT-3 binding and signaling through its cognate receptor TrkC was unaffected by the mutation. These results show that binding of NT-3 to p75LNGFR, TrkA, and TrkB is mediated by a common determinant, which is distinct from that recognized by TrkC and also different and more localized than the one recognized by TrkA and TrkB in their cognate ligands. Thus, although homologous regions in all neurotrophins are used for binding to Trk receptors, a given Trk may actually contact different residues in different neurotrophins. The mutant NT-3 described here may be of greater advantage than native NT-3 when a trophic activity needs to be specifically targeted to TrkC-expressing neurons and provides a monospecific neurotrophin for future therapeutic development.
神经营养因子通过与受体酪氨酸激酶Trk家族成员以及共同的低亲和力受体p75LNGFR结合，来调节脊椎动物神经元的分化和存活。神经营养因子作用的特异性取决于它们与Trk家族不同成员的选择性相互作用；TrkA、TrkB和TrkC分别作为神经生长因子、脑源性神经营养因子和神经营养因子-3（NT-3）的同源受体。与神经生长因子和脑源性神经营养因子不同，NT-3在一定程度上也能结合并激活非同源的TrkA和B受体，尽管这些相互作用的生理相关性尚不清楚。先前的研究表明，神经营养因子利用一个扩展的表面与同源Trk受体结合，而与p75LNGFR的结合则由一组带正电荷的局部残基介导。在此我们表明，NT-3与其非首选受体TrkA和TrkB的结合位点主要由两个带正电荷的残基Arg-31和His-33决定，先前已证明这两个残基构成了与p75LNGFR结合的主要决定因素。将这两个残基同时突变为丙氨酸完全消除了NT-3与TrkA的结合及信号传导，并极大地减少了与TrkB的结合和激活。然而，NT-3通过其同源受体TrkC的结合和信号传导不受该突变影响。这些结果表明，NT-3与p75LNGFR、TrkA和TrkB的结合由一个共同的决定因素介导，该决定因素与TrkC识别的不同，并且与TrkA和TrkB在其同源配体中识别的决定因素也不同且更具局部性。因此，尽管所有神经营养因子中的同源区域都用于与Trk受体结合，但特定的Trk实际上可能与不同神经营养因子中的不同残基接触。当需要将营养活性特异性靶向表达TrkC的神经元时，本文所述的突变型NT-3可能比天然NT-3具有更大优势，并为未来的治疗开发提供了一种单特异性神经营养因子。
