Disulfide-mediated dimerization of L1 Ig domains.
The neural cell adhesion molecule L1 contains immunoglobulin-like (Ig) domains in its extracellular region that mediate homophilic binding, neurite outgrowth and other activities relevant to CNS development. To correlate conformations of these domains to biological function, several L1-Fc fusion proteins whose bioactivities were previously characterized were analyzed by rotary shadowing electron microscopy. We found that bioactive L1-Fcs containing Ig domains 1-4 or 1-6 exhibited extended, branched structures. In contrast, inactive L1-Fcs containing only the first two or three Ig domains assumed compact shapes that suggested interactions between the L1 arms of these proteins. Analysis of an untagged L1 fragment composed of Ig domains 1-3 demonstrated a mixture of monomeric and dimeric forms. Surprisingly, these dimers were stabilized by intermolecular disulfide bonds. Finally, cell surface L1-GFP fusion proteins containing only the first two or three Ig domains in the extracellular region also engaged in disulfide-mediated dimerization. These results suggest a novel mechanism by which mutations in L1 could interfere with its biological functioning.
Haspel
J
J
W.M. Keck Center for Collaborative Neuroscience, Rutgers University, Piscataway, New Jersey 08854-8082, USA.
Schürmann
G
G
Jacob
J
J
Erickson
H P
HP
Grumet
M
M
D001665:Binding Sites / Q000502:physiology; D002490:Central Nervous System / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D019281:Dimerization; D004220:Disulfides / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D007136:Immunoglobulins / Q000378:metabolism* / Q000648:ultrastructure*; D007202:Indicators and Reagents / Q000378:metabolism; D039841:Leukocyte L1 Antigen Complex; D008164:Luminescent Proteins / Q000235:genetics; D008562:Membrane Glycoproteins / Q000378:metabolism* / Q000648:ultrastructure*; D008854:Microscopy, Electron; D009154:Mutation / Q000502:physiology; D009421:Nervous System Malformations / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D019006:Neural Cell Adhesion Molecules / Q000378:metabolism* / Q000648:ultrastructure*; D017510:Protein Folding; D017434:Protein Structure, Tertiary / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000378:metabolism / Q000648:ultrastructure
D004220:Disulfides; D007136:Immunoglobulins; D007202:Indicators and Reagents; D039841:Leukocyte L1 Antigen Complex; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins; D019006:Neural Cell Adhesion Molecules; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins