Garcia Jesus, Gerber Stefan H, Sugita Shuzo, Südhof Thomas C, Rizo Josep
Department of Biochemistry and Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390, USA.
Nat Struct Mol Biol. 2004 Jan;11(1):45-53. doi: 10.1038/nsmb707. Epub 2003 Dec 29.
C2 domains are widespread Ca2+-binding modules. The active zone protein Piccolo (also known as Aczonin) contains an unusual C2A domain that exhibits a low affinity for Ca2+, a Ca2+-induced conformational change and Ca2+-dependent dimerization. We show here that removal of a nine-residue sequence by alternative splicing increases the Ca2+ affinity, abolishes the conformational change and abrogates dimerization of the Piccolo C2A domain. The NMR structure of the Ca2+-free long variant provides a structural basis for these different properties of the two splice forms, showing that the nine-residue sequence forms a beta-strand otherwise occupied by a nonspliced sequence. Consequently, Ca2+-binding to the long Piccolo C2A domain requires a marked rearrangement of secondary structure that cannot occur for the short variant. These results reveal a novel mechanism of action of C2 domains and uncover a structural principle that may underlie the alteration of protein function by short alternatively spliced sequences.
C2结构域是广泛存在的钙离子结合模块。活性区蛋白小突触泡蛋白（也称为Aczonin）含有一个不同寻常的C2A结构域，该结构域对钙离子亲和力低，具有钙离子诱导的构象变化以及钙离子依赖性二聚化作用。我们在此表明，通过可变剪接去除一段九个残基的序列可提高钙离子亲和力，消除构象变化，并消除小突触泡蛋白C2A结构域的二聚化。无钙离子的长变体的核磁共振结构为这两种剪接形式的不同特性提供了结构基础，表明九个残基的序列形成了一条β链，否则该位置会被未剪接的序列占据。因此，钙离子与长的小突触泡蛋白C2A结构域结合需要二级结构发生显著重排，而短变体则不会出现这种情况。这些结果揭示了C2结构域一种新的作用机制，并揭示了一种结构原理，该原理可能是短的可变剪接序列改变蛋白质功能的基础。
