Calcium-binding to lens βB2- and βA3-crystallins suggests that all β-crystallins are calcium-binding proteins

Jobby, Maroor K. ; Sharma, Yogendra (2007) Calcium-binding to lens βB2- and βA3-crystallins suggests that all β-crystallins are calcium-binding proteins FEBS Journal, 274 (16). pp. 4135-4147. ISSN 1742-464X

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Crystallins are the major proteins of a mammalian eye lens. The topologically similar eye lens proteins, β- and γ-crystallins, are the prototype and founding members of the βγ-crystallin superfamily. βγ-Crystallins have until recently been regarded as structural proteins. However, the calcium-binding properties of a few members and the potential role of βγ-crystallins in fertility are being investigated. Because the calcium-binding elements of other member proteins, such as spherulin 3a, are not present in βB2-crystallin and other βγ-crystallins from fish and mammalian genomes, it was argued that lens βγ-crystallins should not bind calcium. In order to probe whether β-crystallins can bind calcium, we selected one basic (βB2) and one acidic (βA3) β-crystallin for calcium-binding studies. Using calcium-binding assays such as 45Ca overlay, terbium binding, Stains-All and isothermal titration calorimetry, we established that both βB2- and βA3-crystallin bind calcium with moderate affinity. There was no significant change in their conformation upon binding calcium as monitored by fluorescence and circular dichroism spectroscopy. However, 15N-1H heteronuclear single quantum correlation NMR spectroscopy revealed that amide environment of several residues underwent changes indicating calcium ligation. With the corroboration of calcium-binding to βB2- and βA3-crystallins, we suggest that all β-crystallins bind calcium. Our results have important implications for understanding the calcium-related cataractogenesis and maintenance of ionic homeostasis in the lens.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
Keywords:βA3-crystallin; βB2-crystallin; βγ-crystallins; Calcium-binding Crystallin; Greek Key Motif
ID Code:50893
Deposited On:27 Jul 2011 13:27
Last Modified:18 May 2016 05:02

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