TAILIEUCHUNG - Báo cáo khoa học: Calcium-binding to lens bB2- and bA3-crystallins suggests that all b-crystallins are calcium-binding proteins

Crystallins are the major proteins of a mammalian eye lens. The topologic-ally similar eye lens proteins,b- and c-crystallins, are the prototype and founding members of the bc-crystallin superfamily. bc-Crystallins have until recently been regarded as structural proteins. However, the calcium-binding properties of a few members and the potential role ofbc-crystallins in fertility are being investigated. | ỊFEBS Journal Calcium-binding to lens pB2- and bA3-crystallins suggests that all b-crystallins are calcium-binding proteins Maroor K. Jobby and Yogendra Sharma Centre for Cellular and Molecular Biology CCMB Hyderabad India Keywords PA3-crystallin PB2-crystallin Py-crystallins calcium-binding crystallin Greek key motif Correspondence Y. Sharma Centre for Cellular and Molecular Biology CCMB UppalRoad Hyderabad 500 007 India Fax 91 40 2716 0591 Tel 91 40 2716 0222 E-mail yogendra@ Received 28 April2007 revised 11 June 2007 accepted 14 June 2007 doi Crystallins are the major proteins of a mammalian eye lens. The topologically similar eye lens proteins P- and y-crystallins are the prototype and founding members of the Py-crystallin superfamily. Py-Crystallins have until recently been regarded as structural proteins. However the calcium-binding properties of a few members and the potential role of Py-crystallins in fertility are being investigated. Because the calcium-binding elements of other member proteins such as spherulin 3 a are not present in pB2-crys-tallin and other Py-crystallins from fish and mammalian genomes it was argued that lens Py-crystallins should not bind calcium. In order to probe whether P-crystallins can bind calcium we selected one basic PB2 and one acidic PA3 P-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 PB2- and PA3-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 hetero-nuclear single quantum correlation NMR spectroscopy revealed that amide environment of several residues underwent changes indicating calcium ligation. With the corroboration of calcium-binding to PB2- and PA3-crys-tallins we suggest that all .

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