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The N‐ and C‐termini of the human Nogo molecules are intrinsically unstructured: Bioinformatics, CD, NMR characterization, and functional implications
Author(s) -
Li Minfen,
Song Jianxing
Publication year - 2007
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.21385
Subject(s) - heteronuclear molecule , chemistry , heteronuclear single quantum coherence spectroscopy , residue (chemistry) , c terminus , nuclear magnetic resonance spectroscopy , structural motif , biochemistry , transmembrane domain , biophysics , microbiology and biotechnology , stereochemistry , biology , amino acid
RTN4 or Nogo proteins are composed of three alternative splice forms, namely 1192‐residue Nogo‐A, 373‐residue Nogo‐B, and 199‐residue Nogo‐C. Nogo proteins have received intense attentions because they have been implicated in a variety of critical cellular processes including CNS neuronal regeneration, vascular remodeling, apoptosis, interaction with β‐amyloid protein converting enzyme, and generation/maintenance of the tubular network of the endoplasmic reticulum (ER). Despite their significantly‐different N‐terminal lengths, they share a conserved C‐terminal reticulon‐homology domain consisting of two transmembrane fragments, a 66‐residue extracellular loop Nogo‐66 and a 38‐residue C‐tail carrying ER retention motif. Nogo‐A owns the largest N‐terminus with 1016 residues while the Nogo‐B has an N‐terminus almost identical to the first 200 residues of Nogo‐A. So far, except for our previous determination of the Nogo‐66 solution structure, no structural characterization of the other Nogo regions has been reported. In the present study, we initiated a systematically investigation of structural properties of Nogo molecules by a combined use of bioinformatics, CD, and NMR spectroscopy. The results led to two striking findings: (1) in agreement with bioinformatics prediction, the N‐ and C‐termini of Nogo‐B were experimentally demonstrated to be intrinsically unstructured by CD, two‐dimensional 1 H 15 N NMR HSQC, hydrogen exchange, and 15 N heteronuclear NOE characterization. (2) Further studies showed that the 1016‐residue N‐terminus of Nogo‐A was again highly disordered. Therefore, it appears that being intrinsically‐unstructured allows Nogo molecules to serve as double‐faceted functional players, with one set of functions involved in cellular signaling processes essential for CNS neuronal regeneration, vascular remodeling, apoptosis and so forth and with another in generating/maintaining membrane‐related structures. We propose that this mechanism may represent a general strategy to place the formation/maintenance of membrane‐related structures under the direct regulation of the cellular signaling. Proteins 2007. © 2007 Wiley‐Liss, Inc.