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Matrix recruitment and calcium sequestration for spatial specific otoconia development.

Yang H, Zhao X, Xu Y, Wang L, He Q, Lundberg YW - PLoS ONE (2011)

Bottom Line: In vivo, the presence of Oc90 in wildtype (wt) mice leads to an enrichment of Ca(2+) in the luminal matrices of the utricle and saccule, whereas absence of Oc90 in the mice leads to drastically reduced matrix-Ca(2+).Molecular modeling and sequence analysis predict structural features that may underlie the interaction and Ca(2+)-sequestering ability of these proteins.Together, the data provide a mechanism for the otoconial matrix assembly and the role of this matrix in accumulating micro-environmental Ca(2+) for efficient CaCO(3) crystallization, thus uncover a critical process governing spatial specific otoconia formation.

View Article: PubMed Central - PubMed

Affiliation: Vestibular Neurogenetics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska, United States of America.

ABSTRACT
Otoconia are bio-crystals anchored to the macular sensory epithelium of the utricle and saccule in the inner ear for motion sensing and bodily balance. Otoconia dislocation, degeneration and ectopic calcification can have detrimental effects on balance and vertigo/dizziness, yet the mechanism underlying otoconia formation is not fully understood. In this study, we show that selected matrix components are recruited to form the crystal matrix and sequester Ca(2+) for spatial specific formation of otoconia. Specifically, otoconin-90 (Oc90) binds otolin through both domains (TH and C1q) of otolin, but full-length otolin shows the strongest interaction. These proteins have much higher expression levels in the utricle and saccule than other inner ear epithelial tissues in mice. In vivo, the presence of Oc90 in wildtype (wt) mice leads to an enrichment of Ca(2+) in the luminal matrices of the utricle and saccule, whereas absence of Oc90 in the mice leads to drastically reduced matrix-Ca(2+). In vitro, either Oc90 or otolin can increase the propensity of extracellular matrix to calcify in cell culture, and co-expression has a synergistic effect on calcification. Molecular modeling and sequence analysis predict structural features that may underlie the interaction and Ca(2+)-sequestering ability of these proteins. Together, the data provide a mechanism for the otoconial matrix assembly and the role of this matrix in accumulating micro-environmental Ca(2+) for efficient CaCO(3) crystallization, thus uncover a critical process governing spatial specific otoconia formation.

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Alignment of murine otolin and collagen X-a1 (Col10a1).The collagen-like domain, aka triple helix (TH) domain, of otolin and Col10a1 have a repeating (Gly-X-Y)n (the shaded ‘G’s denote Glycine), where X is frequently Proline and Y hydroxyproline. The TH domain starts at residue 130 and ends at residue 342 in otolin. The C-terminal globular C1q (gC1q) domain starts at residue 343 in otolin. In collagen, this domain is also known as the non-collagenous NC1 domain. The two D's (blue) denote aspartic acids in Col10a1 that provide the ligands for a cluster of four Ca2+ ions. These residues are conserved in otolin. The inter-subunit contacts are almost entirely hydrophobic with key contact residues highlighted in yellow. Most of these residues are conserved in otolin. Residues 1–23 in otolin and 1–18 in Col10a1 are the signal peptides, respectively; residues 19–56 in Col10a1 is the non-collagenous NC2 domain, and 24–36 in otolin is the residual NC2-like domain. * : . indicate identical residues, conservative and semi-conservative variations, respectively, between otolin and Col10a1.
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pone-0020498-g006: Alignment of murine otolin and collagen X-a1 (Col10a1).The collagen-like domain, aka triple helix (TH) domain, of otolin and Col10a1 have a repeating (Gly-X-Y)n (the shaded ‘G’s denote Glycine), where X is frequently Proline and Y hydroxyproline. The TH domain starts at residue 130 and ends at residue 342 in otolin. The C-terminal globular C1q (gC1q) domain starts at residue 343 in otolin. In collagen, this domain is also known as the non-collagenous NC1 domain. The two D's (blue) denote aspartic acids in Col10a1 that provide the ligands for a cluster of four Ca2+ ions. These residues are conserved in otolin. The inter-subunit contacts are almost entirely hydrophobic with key contact residues highlighted in yellow. Most of these residues are conserved in otolin. Residues 1–23 in otolin and 1–18 in Col10a1 are the signal peptides, respectively; residues 19–56 in Col10a1 is the non-collagenous NC2 domain, and 24–36 in otolin is the residual NC2-like domain. * : . indicate identical residues, conservative and semi-conservative variations, respectively, between otolin and Col10a1.

Mentions: Our recent structural analysis of Oc90 shows that some functionally critical features can be modeled and predicted from known crystal structures of their homologs and paralogs [9], although a co-crystal structure is necessary to know if the Oc90-otolin complex goes through a significant conformational change upon contact. Here we utilized the high degree of sequence similarity between otolin (Swiss-Prot id Q4ZJM7) and type X collagen (Col10a1) (Swiss-Prot id Q05306) (Figure 6) and modeled the tertiary structures. Both proteins belong to a subgroup of the collagen family and the C1q super-family (the two families have overlapping subgroups). Otolin has 74 characteristic Gly-X-Y repeats and Col10a1 has 129 Gly-X-Y repeats in the collagen-like domain, where X is frequently Proline (Pro) and Y hydroxyproline in collagen. Otolin has fewer Pro residues, with 36 total Pro and 15 in Gly-X-Y repeats. Nevertheless, molecular modeling shows that the TH domain of otolin resembles the structure of human COL10A1 [43]: it also has a linear architecture with a flexible and dynamic structure and will likely form a triple helix.


Matrix recruitment and calcium sequestration for spatial specific otoconia development.

Yang H, Zhao X, Xu Y, Wang L, He Q, Lundberg YW - PLoS ONE (2011)

Alignment of murine otolin and collagen X-a1 (Col10a1).The collagen-like domain, aka triple helix (TH) domain, of otolin and Col10a1 have a repeating (Gly-X-Y)n (the shaded ‘G’s denote Glycine), where X is frequently Proline and Y hydroxyproline. The TH domain starts at residue 130 and ends at residue 342 in otolin. The C-terminal globular C1q (gC1q) domain starts at residue 343 in otolin. In collagen, this domain is also known as the non-collagenous NC1 domain. The two D's (blue) denote aspartic acids in Col10a1 that provide the ligands for a cluster of four Ca2+ ions. These residues are conserved in otolin. The inter-subunit contacts are almost entirely hydrophobic with key contact residues highlighted in yellow. Most of these residues are conserved in otolin. Residues 1–23 in otolin and 1–18 in Col10a1 are the signal peptides, respectively; residues 19–56 in Col10a1 is the non-collagenous NC2 domain, and 24–36 in otolin is the residual NC2-like domain. * : . indicate identical residues, conservative and semi-conservative variations, respectively, between otolin and Col10a1.
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Related In: Results  -  Collection

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pone-0020498-g006: Alignment of murine otolin and collagen X-a1 (Col10a1).The collagen-like domain, aka triple helix (TH) domain, of otolin and Col10a1 have a repeating (Gly-X-Y)n (the shaded ‘G’s denote Glycine), where X is frequently Proline and Y hydroxyproline. The TH domain starts at residue 130 and ends at residue 342 in otolin. The C-terminal globular C1q (gC1q) domain starts at residue 343 in otolin. In collagen, this domain is also known as the non-collagenous NC1 domain. The two D's (blue) denote aspartic acids in Col10a1 that provide the ligands for a cluster of four Ca2+ ions. These residues are conserved in otolin. The inter-subunit contacts are almost entirely hydrophobic with key contact residues highlighted in yellow. Most of these residues are conserved in otolin. Residues 1–23 in otolin and 1–18 in Col10a1 are the signal peptides, respectively; residues 19–56 in Col10a1 is the non-collagenous NC2 domain, and 24–36 in otolin is the residual NC2-like domain. * : . indicate identical residues, conservative and semi-conservative variations, respectively, between otolin and Col10a1.
Mentions: Our recent structural analysis of Oc90 shows that some functionally critical features can be modeled and predicted from known crystal structures of their homologs and paralogs [9], although a co-crystal structure is necessary to know if the Oc90-otolin complex goes through a significant conformational change upon contact. Here we utilized the high degree of sequence similarity between otolin (Swiss-Prot id Q4ZJM7) and type X collagen (Col10a1) (Swiss-Prot id Q05306) (Figure 6) and modeled the tertiary structures. Both proteins belong to a subgroup of the collagen family and the C1q super-family (the two families have overlapping subgroups). Otolin has 74 characteristic Gly-X-Y repeats and Col10a1 has 129 Gly-X-Y repeats in the collagen-like domain, where X is frequently Proline (Pro) and Y hydroxyproline in collagen. Otolin has fewer Pro residues, with 36 total Pro and 15 in Gly-X-Y repeats. Nevertheless, molecular modeling shows that the TH domain of otolin resembles the structure of human COL10A1 [43]: it also has a linear architecture with a flexible and dynamic structure and will likely form a triple helix.

Bottom Line: In vivo, the presence of Oc90 in wildtype (wt) mice leads to an enrichment of Ca(2+) in the luminal matrices of the utricle and saccule, whereas absence of Oc90 in the mice leads to drastically reduced matrix-Ca(2+).Molecular modeling and sequence analysis predict structural features that may underlie the interaction and Ca(2+)-sequestering ability of these proteins.Together, the data provide a mechanism for the otoconial matrix assembly and the role of this matrix in accumulating micro-environmental Ca(2+) for efficient CaCO(3) crystallization, thus uncover a critical process governing spatial specific otoconia formation.

View Article: PubMed Central - PubMed

Affiliation: Vestibular Neurogenetics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska, United States of America.

ABSTRACT
Otoconia are bio-crystals anchored to the macular sensory epithelium of the utricle and saccule in the inner ear for motion sensing and bodily balance. Otoconia dislocation, degeneration and ectopic calcification can have detrimental effects on balance and vertigo/dizziness, yet the mechanism underlying otoconia formation is not fully understood. In this study, we show that selected matrix components are recruited to form the crystal matrix and sequester Ca(2+) for spatial specific formation of otoconia. Specifically, otoconin-90 (Oc90) binds otolin through both domains (TH and C1q) of otolin, but full-length otolin shows the strongest interaction. These proteins have much higher expression levels in the utricle and saccule than other inner ear epithelial tissues in mice. In vivo, the presence of Oc90 in wildtype (wt) mice leads to an enrichment of Ca(2+) in the luminal matrices of the utricle and saccule, whereas absence of Oc90 in the mice leads to drastically reduced matrix-Ca(2+). In vitro, either Oc90 or otolin can increase the propensity of extracellular matrix to calcify in cell culture, and co-expression has a synergistic effect on calcification. Molecular modeling and sequence analysis predict structural features that may underlie the interaction and Ca(2+)-sequestering ability of these proteins. Together, the data provide a mechanism for the otoconial matrix assembly and the role of this matrix in accumulating micro-environmental Ca(2+) for efficient CaCO(3) crystallization, thus uncover a critical process governing spatial specific otoconia formation.

Show MeSH
Related in: MedlinePlus