Abstract
Olfactomedin-1 (Olfm1; also known as noelin and pancortin) is a member of the olfactomedin domain-containing superfamily and a highly expressed neuronal glycoprotein important for nervous system development. It binds a number of secreted proteins and cell surface-bound receptors to induce cell signaling processes. Using a combined approach of x-ray crystallography, solution scattering, analytical ultracentrifugation, and electron microscopy we determined that full-length Olfm1 forms disulfide-linked tetramers with a distinctive V-shaped architecture. The base of the "V" is formed by two disulfide-linked dimeric N-terminal domains. Each of the two V legs consists of a parallel dimeric disulfide-linked coiled coil with a C-terminal β-propeller dimer at the tips. This agrees with our crystal structure of a C-terminal coiled-coil segment and β-propeller combination (Olfm1(coil-Olf)) that reveals a disulfide-linked dimeric arrangement with the β-propeller top faces in an outward exposed orientation. Similar to its family member myocilin, Olfm1 is stabilized by calcium. The dimer-of-dimers architecture suggests a role for Olfm1 in clustering receptors to regulate signaling and sheds light on the conformation of several other olfactomedin domain family members.
Highlights
Olfactomedin-1 (Olfm1) is a secreted protein with diverse roles in the developing nervous system
Using a combined approach of x-ray crystallography, solution scattering, analytical ultracentrifugation, and electron microscopy we determined that full-length Olfm1 forms disulfide-linked tetramers with a distinctive V-shaped architecture
Olfm1 Forms Disulfide-linked Homotetramers—Recombinantly expressed Olfm1 lacking the C-terminal endoplasmic reticulum retention signal was purified from HEK293 supernatant for structural studies
Summary
Olfactomedin-1 (Olfm1) is a secreted protein with diverse roles in the developing nervous system. Olfactomedin-1 (Olfm; known as noelin and pancortin) is a member of the olfactomedin domain-containing superfamily and a highly expressed neuronal glycoprotein important for nervous system development It binds a number of secreted proteins and cell surface-bound receptors to induce cell signaling processes. The most complete isoform of Olfm, isoform 1 ( called BMZ), is most similar to the other Olfm paralogs This isoform comprises a disulfide-containing C-terminal olfactomedin domain, which has recently been shown to be a five-bladed -propeller in myocilin, gliomedin, and latrophilin (14 –16). We determined the structure of the olfactomedin domain of Olfm and the quaternary arrangement and architecture of the full-length protein using a combined approach of x-ray crystallography, electron microscopy, and biophysical characterization
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