title: Combinatorial homophilic interaction between gamma-protocadherin multimers greatly expands the molecular diversity of cell adhesion.
abstract: The specificity of interactions between neurons is believed to be mediated by diverse cell adhesion molecules, including members of the cadherin superfamily. Whereas mechanisms of classical cadherin adhesion have been studied extensively, much less is known about the related protocadherins (Pcdhs), which together make up the majority of the superfamily. Here we use quantitative cell aggregation assays and biochemical analyses to characterize cis and trans interactions among the 22-member gamma-Pcdh family, which have been shown to be critical for the control of synaptogenesis and neuronal survival. We show that gamma-Pcdh isoforms engage in trans interactions that are strictly homophilic. In contrast to classical cadherins, gamma-Pcdh interactions are only partially Ca(2+)-dependent, and their specificity is mediated through the second and third extracellular cadherin (EC) domains (EC2 and EC3), rather than through EC1. The gamma-Pcdhs also interact both covalently and noncovalently in the cis-orientation to form multimers both in vitro and in vivo. In contrast to gamma-Pcdh trans interactions, cis interactions are highly promiscuous, with no isoform specificity. We present data supporting a model in which gamma-Pcdh cis-tetramers represent the unit of their adhesive trans interactions. Unrestricted tetramerization in cis, coupled with strictly homophilic interactions in trans, predicts that the 22 gamma-Pcdhs could form 234,256 distinct adhesive interfaces. Given the demonstrated role of the gamma-Pcdhs in synaptogenesis, our data have important implications for the molecular control of neuronal specificity.
authors.affiliation: Department of Biology, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Dietmar
authors.initials: D
authors.lastname: Schreiner
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Weiner
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D019556:COS Cells; D000070585:Cadherin Related Proteins; D015820:Cadherins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002448:Cell Adhesion; D002450:Cell Communication; D002460:Cell Line; D002522:Chlorocebus aethiops; D005455:Fluorescent Antibody Technique; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007365:Intercellular Junctions / Q000378:metabolism*; D020014:K562 Cells; D051379:Mice; D009154:Mutation; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D014162:Transfection
chemical_list: D000070585:Cadherin Related Proteins; D015820:Cadherins; C464785:Gamma-protocadherins; D020033:Protein Isoforms; D049452:Green Fluorescent Proteins