title: A Partial Calcium-Free Linker Confers Flexibility to Inner-Ear Protocadherin-15.
abstract: Tip links of the inner ear are protein filaments essential for hearing and balance. Two atypical cadherins, cadherin-23 and protocadherin-15, interact in a Ca2+-dependent manner to form tip links. The largely unknown structure and mechanics of these proteins are integral to understanding how tip links pull on ion channels to initiate sensory perception. Protocadherin-15 has 11 extracellular cadherin (EC) repeats. Its EC3-4 linker lacks several of the canonical Ca2+-binding residues, and contains an aspartate-to-alanine polymorphism (D414A) under positive selection in East Asian populations. We present structures of protocadherin-15 EC3-5 featuring two Ca2+-binding linker regions: canonical EC4-5 linker binding three Ca2+ions, and non-canonical EC3-4 linker binding only two Ca2+ions. Our structures and biochemical assays reveal little difference between the D414 and D414A variants. Simulations predict that the partial Ca2+-free EC3-4 linker exhibits increased flexural flexibility without compromised mechanical strength, providing insight into the dynamics of tip links and other atypical cadherins.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, 52 Oxford Street, Cambridge, MA 02138, USA; Biophysics Graduate Program, Harvard University, Boston, MA 02115, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Powers
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, 52 Oxford Street, Cambridge, MA 02138, USA. Electronic address: gaudet@mcb.harvard.edu.
authors.forename: Rachelle
authors.initials: R
authors.lastname: Gaudet
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University, 484 West 12(th) Avenue, Columbus, OH 43210, USA. Electronic address: sotomayor.8@osu.edu.
authors.forename: Marcos
authors.initials: M
authors.lastname: Sotomayor
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D000070585:Cadherin Related Proteins; D015820:Cadherins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D007758:Ear, Inner / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D020641:Polymorphism, Single Nucleotide; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: C498835:CDHR15, human; D000070585:Cadherin Related Proteins; D015820:Cadherins; D002118:Calcium
keywords: X-ray crystallography; cadherin superfamily; deafness; hearing; mechanotransduction; molecular dynamics simulation; tip link