Journal of Biological Chemistry
Volume 272, Issue 35, 29 August 1997, Pages 22182-22190
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PROTEIN CHEMISTRY AND STRUCTURE
Calcium-dependent Binding of Sorcin to the N-terminal Domain of Synexin (Annexin VII)*

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The annexins are characterized by their ability to bind phospholipid membranes in a Ca2+-dependent manner. Sequence variability between the N-terminal domains of the family members may contribute to the specific cellular function of each annexin. To identify proteins that interact with the N-terminal domain of synexin (annexin VII), a fusion protein was constructed composed of glutathioneS-transferase fused to amino acids 1–145 of human synexin. Affinity chromatography using this construct identified sorcin as a Ca2+-dependent synexin-binding protein. Overlay assays confirmed the interaction. The glutathioneS-transferase construct associates with recombinant sorcin over the range of pCa2+ = 4.7–3.1 with no binding observed at pCa2+ = 5.4. Overlay assays using deletion constructs of the synexin N-terminal domain mapped the sorcin binding site to the N-terminal 31 amino acids of the synexin protein. Additionally, synexin forms a complex with sorcin and recruits this protein to chromaffin granule membranes in a Ca2+-dependent manner. Sorcin is able to inhibit synexin-mediated chromaffin granule aggregation in a manner saturable with increasing sorcin concentrations, but does not influence the Ca2+ sensitivity of synexin-mediated granule aggregation. Therefore, the interaction between sorcin and synexin may serve to regulate the functions of these proteins on membrane surfaces in a Ca2+-dependent manner.

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*

This work was supported by National Institutes of Health Grant GM53266.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.