Woods Amina S, Marcellino Daniel, Jackson Shelley N, Franco Rafael, Ferré Sergi, Agnati Luigi F, Fuxe Kjell
National Institute on Drug Abuse, IRP, NIH, DHHS, Baltimore, MD 21224, USA.
J Proteome Res. 2008 Aug;7(8):3428-34. doi: 10.1021/pr8001782. Epub 2008 Jul 1.
Receptor heteromerization is a mechanism used by G protein-coupled receptors to diversify their properties and function. We previously demonstrated that these interactions occur through salt bridge formation between epitopes of the involved receptors. Recent studies claim that calmodulin (CaM) binds to an Arg-rich epitope located in the amino-terminus of the dopamine D(2) receptor third intracellular loop. This is the same epitope involved in adenosine A(2A)-D(2) receptor heteromerization, through Coulombic interaction between the Arg residues and a phosphorylated serine (pS) located in the medial segment of the C-terminus of the A(2A) receptor. Mass spectrometric analysis indicates that an electrostatic interaction involving the D(2) receptor Arg-rich epitope and several CaM acidic epitopes are mainly responsible for the D(2) receptor-CaM binding. CaM could also form multiple noncovalent complexes by means of electrostatic interactions with an epitope localized in the proximal segment of the C-terminus of the A(2A) receptor. Ca(2+) disrupted the binding of CaM to the D(2) but not to the A(2A) receptor epitope, and CaM disrupted the electrostatic interactions between the D(2) receptor epitope and the more distal A(2A) receptor epitope. A model is introduced with the possible functional implications of A(2A)-D(2)-CaM interactions. These in vitro findings imply a possible regulatory role for CaM in receptor heteromers formation.
受体异聚化是G蛋白偶联受体用于使其特性和功能多样化的一种机制。我们之前证明这些相互作用是通过所涉及受体表位之间形成盐桥而发生的。最近的研究表明钙调蛋白（CaM）与位于多巴胺D(2)受体第三细胞内环氨基末端的富含精氨酸的表位结合。这与腺苷A(2A)-D(2)受体异聚化中涉及的表位相同，通过精氨酸残基与位于A(2A)受体C末端中间段的磷酸化丝氨酸（pS）之间的库仑相互作用实现。质谱分析表明，涉及D(2)受体富含精氨酸表位和几个CaM酸性表位的静电相互作用是D(2)受体与CaM结合的主要原因。CaM还可通过与位于A(2A)受体C末端近端段的一个表位的静电相互作用形成多个非共价复合物。Ca(2+)破坏了CaM与D(2)受体的结合，但不影响其与A(2A)受体表位的结合，并且CaM破坏了D(2)受体表位与更远端的A(2A)受体表位之间的静电相互作用。本文引入了一个关于A(2A)-D(2)-CaM相互作用可能功能意义的模型。这些体外研究结果暗示CaM在受体异聚体形成中可能具有调节作用。
