title: Structural model for the mannose receptor family uncovered by electron microscopy of Endo180 and the mannose receptor.
abstract: The mannose receptor family comprises four members in mammals, Endo180 (CD280), DEC-205 (CD205), phospholipase A(2) receptor (PLA(2)R) and the mannose receptor (MR, CD206), whose extracellular portion contains a similar domain arrangement: an N-terminal cysteine-rich domain (CysR) followed by a single fibronectin type II domain (FNII) and 8-10 C-type lectin-like domains (CTLDs). These proteins mediate diverse functions ranging from extracellular matrix turnover through collagen uptake to homeostasis and immunity based on sugar recognition. Endo180 and the MR are multivalent transmembrane receptors capable of interacting with multiple ligands; in both receptors FNII recognizes collagens, and a single CTLD retains lectin activity (CTLD2 in Endo180 and CTLD4 in MR). It is expected that the overall conformation of these multivalent molecules would deeply influence their function as the availability of their binding sites could be altered under different conditions. However, conflicting reports have been published on the three-dimensional arrangement of these receptors. Here, we have used single particle electron microscopy to elucidate the three-dimensional organization of the MR and Endo180. Strikingly, we have found that both receptors display distinct three-dimensional structures, which are, however, conceptually very similar: a bent and compact conformation built upon interactions of the CysR domain and the lone functional CTLD. Biochemical and electron microscopy experiments indicate that, under a low pH mimicking the endosomal environment, both MR and Endo180 experience large conformational changes. We propose a structural model for the mannose receptor family where at least two conformations exist that may serve to regulate differences in ligand selectivity.
authors.affiliation: Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu, 9, Campus Universidad Complutense, 28040 Madrid, Spain.
authors.forename: Jasminka
authors.initials: J
authors.lastname: Boskovic
authors.forename: James N
authors.initials: JN
authors.lastname: Arnold
authors.forename: Richard
authors.initials: R
authors.lastname: Stilion
authors.forename: Siamon
authors.initials: S
authors.lastname: Gordon
authors.forename: Robert B
authors.initials: RB
authors.lastname: Sim
authors.forename: Angel
authors.initials: A
authors.lastname: Rivera-Calzada
authors.forename: Dirk
authors.initials: D
authors.lastname: Wienke
authors.forename: Clare M
authors.initials: CM
authors.lastname: Isacke
authors.forename: Luisa
authors.initials: L
authors.lastname: Martinez-Pomares
authors.forename: Oscar
authors.initials: O
authors.lastname: Llorca
mesh_terms: D006863:Hydrogen-Ion Concentration; D021621:Imaging, Three-Dimensional; D037181:Lectins, C-Type / Q000737:chemistry* / Q000648:ultrastructure*; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins / Q000737:chemistry* / Q000648:ultrastructure*; D008854:Microscopy, Electron; D008961:Models, Structural; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000648:ultrastructure*; D011975:Receptors, Mitogen / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: C408294:Endo180; D037181:Lectins, C-Type; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D011956:Receptors, Cell Surface; D011975:Receptors, Mitogen