Cell Adhesion Molecule L1 in Folded (horseshoe) and Extended Conformations
Overview
Molecular Biology
Authors
Affiliations
We have investigated the structure of the cell adhesion molecule L1 by electron microscopy. We were particularly interested in the conformation of the four N-terminal immunoglobulin domains, because x-ray diffraction showed that these domains are bent into a horseshoe shape in the related molecules hemolin and axonin-1. Surprisingly, rotary-shadowed specimens showed the molecules to be elongated, with no indication of the horseshoe shape. However, sedimentation data suggested that these domains of L1 were folded into a compact shape in solution; therefore, this prompted us to look at the molecules by an alternative technique, negative stain. The negative stain images showed a compact shape consistent with the expected horseshoe conformation. We speculate that in rotary shadowing the contact with the mica caused a distortion of the protein, weakening the bonds forming the horseshoe and permitting the molecule to extend. We have thus confirmed that the L1 molecule is primarily in the horseshoe conformation in solution, and we have visualized for the first time its opening into an extended conformation. Our study resolves conflicting interpretations from previous electron microscopy studies of L1.
Chataigner L, Leloup N, Janssen B Front Mol Biosci. 2020; 7:129.
PMID: 32850948 PMC: 7427315. DOI: 10.3389/fmolb.2020.00129.
Molecular Mechanism of MDGA1: Regulation of Neuroligin 2:Neurexin Trans-synaptic Bridges.
Gangwar S, Zhong X, Seshadrinathan S, Chen H, Machius M, Rudenko G Neuron. 2017; 94(6):1132-1141.e4.
PMID: 28641112 PMC: 5745067. DOI: 10.1016/j.neuron.2017.06.009.
Patzke C, Acuna C, Giam L, Wernig M, Sudhof T J Exp Med. 2016; 213(4):499-515.
PMID: 27001749 PMC: 4821644. DOI: 10.1084/jem.20150951.
An extracellular adhesion molecule complex patterns dendritic branching and morphogenesis.
Dong X, Liu O, Howell A, Shen K Cell. 2013; 155(2):296-307.
PMID: 24120131 PMC: 3927720. DOI: 10.1016/j.cell.2013.08.059.
Chacon-Martinez C, Kiessling N, Winterhoff M, Faix J, Muller-Reichert T, Jessberger R J Biol Chem. 2013; 288(40):28687-703.
PMID: 23921380 PMC: 3789966. DOI: 10.1074/jbc.M113.461277.