TAILIEUCHUNG - Báo cáo khoa học: Ion-binding properties of Calnuc, Ca2+ versus Mg2+ – Calnuc adopts additional and unusual Ca2+-binding sites upon interaction with G-protein

Calnuc is a novel, highly modular, EF-hand containing, Ca 2+ -binding, Golgi resident protein whose functions are not clear. Using amino acid sequences, we demonstrate that Calnuc is a highly conserved protein among various organisms, from Ciona intestinalisto humans. Maximum homology among all sequences is found in the region that binds to G-pro-teins. | ỊFEBS Journal Ion-binding properties of Calnuc Ca2 versus Mg2 - Calnuc adopts additional and unusual Ca2 -binding sites upon interaction with G-protein Madhavi Kanuru Jebakumar J. Samuel Lavanya M. Balivada and Gopala K. Aradhyam Department of Biotechnology Indian Institute of Technology Madras Chennai India Keywords Ca2 binding Calnuc G-proteins protein-protein interactions Stains-all Correspondence G. K. Aradhyam Department of Biotechnology Indian Institute of Technology Madras Chennai 600036 India Fax 91 44 22574102 Tel 91 44 22574112 E-mail agk@ These authors contributed equally to this work Received 14 November 2008 revised 17 February 2009 accepted 20 February 2009 doi Calnuc is a novel highly modular EF-hand containing Ca2 -binding Golgi resident protein whose functions are not clear. Using amino acid sequences we demonstrate that Calnuc is a highly conserved protein among various organisms from Ciona intestinalis to humans. Maximum homology among all sequences is found in the region that binds to G-pro-teins. In humans it is known to be expressed in a variety of tissues and it interacts with several important protein partners. Among other proteins Calnuc is known to interact with heterotrimeric G-proteins specifically with the a-subunit. Herein we report the structural implications of Ca2 and Mg2 binding and illustrate that Calnuc functions as a downstream effector for G-protein a-subunit. Our results show that Ca2 binds with an affinity of 7 IM and causes structural changes. Although Mg2 binds to Calnuc with very weak affinity the structural changes that it causes are further enhanced by Ca2 binding. Furthermore isothermal titration calorimetry results show that Calnuc and the G-protein bind with an affinity of 13 nM. We also predict a probable function for Calnuc that of maintaining Ca2 homeostasis in the cell. Using Stains-all and terbium as Ca2 mimic probes we demonstrate that the Ca2 -binding ability of Calnuc

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