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A Novel C-Terminal CIB2 (Calcium and Integrin Binding Protein 2) Mutation Associated with Non-Syndromic Hearing Loss in a Hispanic Family.

Patel K, Giese AP, Grossheim JM, Hegde RS, Hegde RS, Delio M, Samanich J, Riazuddin S, Frolenkov GI, Cai J, Ahmed ZM, Morrow BE - PLoS ONE (2015)

Bottom Line: The carboxy-termini of CIB proteins are associated with calcium binding and intracellular signaling.Our ex vivo studies revealed that the mutation did not alter the interactions of CIB2 with Whirlin, nor its targeting to the tips of hair cell stereocilia.However, we found that the mutation disrupts inhibition of ATP-induced Ca2+ responses by CIB2 in a heterologous expression system.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Albert Einstein College of Medicine, 1301 Morris Park Avenue, Bronx, New York, United States of America.

ABSTRACT
Hearing loss is a complex disorder caused by both genetic and environmental factors. Previously, mutations in CIB2 have been identified as a common cause of genetic hearing loss in Pakistani and Turkish populations. Here we report a novel (c.556C>T; p.(Arg186Trp)) transition mutation in the CIB2 gene identified through whole exome sequencing (WES) in a Caribbean Hispanic family with non-syndromic hearing loss. CIB2 belongs to the family of calcium-and integrin-binding (CIB) proteins. The carboxy-termini of CIB proteins are associated with calcium binding and intracellular signaling. The p.(Arg186Trp) mutation is localized within predicted type II PDZ binding ligand at the carboxy terminus. Our ex vivo studies revealed that the mutation did not alter the interactions of CIB2 with Whirlin, nor its targeting to the tips of hair cell stereocilia. However, we found that the mutation disrupts inhibition of ATP-induced Ca2+ responses by CIB2 in a heterologous expression system. Our findings support p.(Arg186Trp) mutation as a cause for hearing loss in this Hispanic family. In addition, it further highlights the necessity of the calcium binding property of CIB2 for normal hearing.

No MeSH data available.


Related in: MedlinePlus

The C-terminal helix of CIB2 mutation may be destabilized because of steric hindrance.Molecular models using the Protein Data Bank (PDB) 1XO5 crystal structure of Ca2+-CIB1 as a template. A) The backbone ribbon of the C-terminal helix of CIB1 is highlighted in red, and the four Ca2+ ions are represented by white spheres. B) The side-chain of the Arg186 residue is represented in white and blue (dash line), and the Trp residue is overlapped in green at position 186.
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pone.0133082.g006: The C-terminal helix of CIB2 mutation may be destabilized because of steric hindrance.Molecular models using the Protein Data Bank (PDB) 1XO5 crystal structure of Ca2+-CIB1 as a template. A) The backbone ribbon of the C-terminal helix of CIB1 is highlighted in red, and the four Ca2+ ions are represented by white spheres. B) The side-chain of the Arg186 residue is represented in white and blue (dash line), and the Trp residue is overlapped in green at position 186.

Mentions: We analyzed the effect of the p.Arg186Trp mutation on the molecular structure of CIB2, using the human crystal structure of CIB1 (1XO5) as a template. The carboxy terminal helix of CIB1 is flexible and believed to participate in the Ca2+ binding. This helix is folded back against the hydrophobic integrin binding pocket of the CIB1, C-domain in the 1XO5.PDB crystal structure. The displacement of this helix is also part of the integrin binding mechanism suggesting that it might affect access to the hydrophobic pocket to integrins. Any unfolding or destabilization of the helix due to p.Arg186Trp allele could potentially affect the ability for CIB2 to bind to calcium or integrins (Fig 6). To test if the pArg186Trp mutation affects the calcium binding affinity of CIB2, we measured the inositol triphosphate (IP3)-dependent Ca2+ responses evoked by extracellular ATP in HEK-293 cells transiently transfected with Dsred tagged constructs (Fig 7). As a control we measured responses in the cells expressing the p.Phe91Ser variant of CIB2 [30]. HEK-293 cells overexpressing wild type CIB2 demonstrated significantly decreased ATP-induced Ca2+ responses as compared to no Ca2+ buffering ability in mock transfected cells, as previously reported [30]. Cells transfected with the p.Phe91Ser mutant allele did not alter the calcium binding affinity of CIB2 (Fig 7). Intriguingly, HEK-293 cells overexpressing p.Arg186Trp mutant CIB2 had a significant increase in Ca2+ responses, indicating that this CIB2R186W variant resulted in loss of Ca2+ sequestering ability (Fig 7).


A Novel C-Terminal CIB2 (Calcium and Integrin Binding Protein 2) Mutation Associated with Non-Syndromic Hearing Loss in a Hispanic Family.

Patel K, Giese AP, Grossheim JM, Hegde RS, Hegde RS, Delio M, Samanich J, Riazuddin S, Frolenkov GI, Cai J, Ahmed ZM, Morrow BE - PLoS ONE (2015)

The C-terminal helix of CIB2 mutation may be destabilized because of steric hindrance.Molecular models using the Protein Data Bank (PDB) 1XO5 crystal structure of Ca2+-CIB1 as a template. A) The backbone ribbon of the C-terminal helix of CIB1 is highlighted in red, and the four Ca2+ ions are represented by white spheres. B) The side-chain of the Arg186 residue is represented in white and blue (dash line), and the Trp residue is overlapped in green at position 186.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4591343&req=5

pone.0133082.g006: The C-terminal helix of CIB2 mutation may be destabilized because of steric hindrance.Molecular models using the Protein Data Bank (PDB) 1XO5 crystal structure of Ca2+-CIB1 as a template. A) The backbone ribbon of the C-terminal helix of CIB1 is highlighted in red, and the four Ca2+ ions are represented by white spheres. B) The side-chain of the Arg186 residue is represented in white and blue (dash line), and the Trp residue is overlapped in green at position 186.
Mentions: We analyzed the effect of the p.Arg186Trp mutation on the molecular structure of CIB2, using the human crystal structure of CIB1 (1XO5) as a template. The carboxy terminal helix of CIB1 is flexible and believed to participate in the Ca2+ binding. This helix is folded back against the hydrophobic integrin binding pocket of the CIB1, C-domain in the 1XO5.PDB crystal structure. The displacement of this helix is also part of the integrin binding mechanism suggesting that it might affect access to the hydrophobic pocket to integrins. Any unfolding or destabilization of the helix due to p.Arg186Trp allele could potentially affect the ability for CIB2 to bind to calcium or integrins (Fig 6). To test if the pArg186Trp mutation affects the calcium binding affinity of CIB2, we measured the inositol triphosphate (IP3)-dependent Ca2+ responses evoked by extracellular ATP in HEK-293 cells transiently transfected with Dsred tagged constructs (Fig 7). As a control we measured responses in the cells expressing the p.Phe91Ser variant of CIB2 [30]. HEK-293 cells overexpressing wild type CIB2 demonstrated significantly decreased ATP-induced Ca2+ responses as compared to no Ca2+ buffering ability in mock transfected cells, as previously reported [30]. Cells transfected with the p.Phe91Ser mutant allele did not alter the calcium binding affinity of CIB2 (Fig 7). Intriguingly, HEK-293 cells overexpressing p.Arg186Trp mutant CIB2 had a significant increase in Ca2+ responses, indicating that this CIB2R186W variant resulted in loss of Ca2+ sequestering ability (Fig 7).

Bottom Line: The carboxy-termini of CIB proteins are associated with calcium binding and intracellular signaling.Our ex vivo studies revealed that the mutation did not alter the interactions of CIB2 with Whirlin, nor its targeting to the tips of hair cell stereocilia.However, we found that the mutation disrupts inhibition of ATP-induced Ca2+ responses by CIB2 in a heterologous expression system.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, Albert Einstein College of Medicine, 1301 Morris Park Avenue, Bronx, New York, United States of America.

ABSTRACT
Hearing loss is a complex disorder caused by both genetic and environmental factors. Previously, mutations in CIB2 have been identified as a common cause of genetic hearing loss in Pakistani and Turkish populations. Here we report a novel (c.556C>T; p.(Arg186Trp)) transition mutation in the CIB2 gene identified through whole exome sequencing (WES) in a Caribbean Hispanic family with non-syndromic hearing loss. CIB2 belongs to the family of calcium-and integrin-binding (CIB) proteins. The carboxy-termini of CIB proteins are associated with calcium binding and intracellular signaling. The p.(Arg186Trp) mutation is localized within predicted type II PDZ binding ligand at the carboxy terminus. Our ex vivo studies revealed that the mutation did not alter the interactions of CIB2 with Whirlin, nor its targeting to the tips of hair cell stereocilia. However, we found that the mutation disrupts inhibition of ATP-induced Ca2+ responses by CIB2 in a heterologous expression system. Our findings support p.(Arg186Trp) mutation as a cause for hearing loss in this Hispanic family. In addition, it further highlights the necessity of the calcium binding property of CIB2 for normal hearing.

No MeSH data available.


Related in: MedlinePlus