Paired octamer rings of retinoschisin suggest a junctional model for cell-cell adhesion in the retina.
Retinoschisin (RS1) is involved in cell-cell junctions in the retina, but is unique among known cell-adhesion proteins in that it is a soluble secreted protein. Loss-of-function mutations in RS1 lead to early vision impairment in young males, called X-linked retinoschisis. The disease is characterized by separation of inner retinal layers and disruption of synaptic signaling. Using cryo-electron microscopy, we report the structure at 4.1 Å, revealing double octamer rings not observed before. Each subunit is composed of a discoidin domain and a small N-terminal (RS1) domain. The RS1 domains occupy the centers of the rings, but are not required for ring formation and are less clearly defined, suggesting mobility. We determined the structure of the discoidin rings, consistent with known intramolecular and intermolecular disulfides. The interfaces internal to and between rings feature residues implicated in X-linked retinoschisis, indicating the importance of correct assembly. Based on this structure, we propose that RS1 couples neighboring membranes together through octamer-octamer contacts, perhaps modulated by interactions with other membrane components.
Laboratory for Structural Biology Research, National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, MD 20892; Molecular Control and Genetics Section, Gene Regulation and Chromosome Biology Laboratory, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702;
Gökhan
G
Tolun
Section on Translational Research for Retinal and Macular Degeneration, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892;
Camasamudram
C
Vijayasarathy
Laboratory for Structural Biology Research, National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, MD 20892; Cryo-Electron Microscopy Facility, Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147;
Rick
R
Huang
Section on Translational Research for Retinal and Macular Degeneration, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892;
Yong
Y
Zeng
Protein/Peptide Sequencing Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892;
Yan
Y
Li
Laboratory for Structural Biology Research, National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, MD 20892;
Alasdair C
AC
Steven
Section on Translational Research for Retinal and Macular Degeneration, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892; National Eye Institute, National Institutes of Health, Bethesda, MD 20892 pas@nei.nih.gov heymannb@mail.nih.gov.
Paul A
PA
Sieving
Laboratory for Structural Biology Research, National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, MD 20892; pas@nei.nih.gov heymannb@mail.nih.gov.
J Bernard
0000-0002-8872-5326
JB
Heymann
D000595:Amino Acid Sequence; D000818:Animals; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000737:chemistry* / Q000648:ultrastructure*; D003198:Computer Simulation; D019281:Dimerization; D005136:Eye Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D007365:Intercellular Junctions / Q000737:chemistry / Q000648:ultrastructure*; D051379:Mice; D008954:Models, Biological; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000648:ultrastructure; D011487:Protein Conformation; D012160:Retina / Q000737:chemistry* / Q000648:ultrastructure*
D015815:Cell Adhesion Molecules; D005136:Eye Proteins; D046912:Multiprotein Complexes; C491843:RS1 protein, mouse
X-linked retinoschisis; cryo-electron microscopy; discoidin domain; retinoschisin; single particle analysis