Prokineticin 2 (PK2) and Prokineticin 2 beta (PK2β), products of alternative splicing of pk2 gene, are chemokine-like proteins. While PK2 mediates its biological activities by signaling with the same efficiency through two homologous G protein coupled receptors, prokineticin receptor 1 (PKR1) and prokineticin receptor 2 (PKR2), PK2β is able to bind specifically PKR1.

Extracellular loop 2 (ECL2) of chemokine receptors is a part of a transmembrane (TM) ligand binding site. In the ECL2 of PKR2 is present, as well as in all chemokine receptors, an aromatic residue cluster, involving tryptophan 212 localized four residues after an ECL2 conserved cysteine, and Phenylalanine 198 located in the top of TM 4.

In this work, the photoactivatable unnatural amino acid p-benzoyl-L-phenylalanine is incorporated by amber codon suppression technology into PKR2 in position 212. Experiments of photoactivatable cross-linking demonstrated the role of tryptophan in position 212 for binding the ligand contacting Tryptophan in position 24. We also analyzed the role of Phenylalanine 198 in the specificity of PKRs binding. The comparison of TM-bundle binding sites between PKR1 and PKR2 revealed that they are completely conserved except for one residue: valine 207 in human PKR1, which is phenylalanine 198 in human PKR2. The F198V mutation in PKR2 permits to obtain a receptor able to bind more efficiently PK2β, a ligand highly specific for PKR1.

PK2基因的可变剪接产物Prokineticin 2（PK2）和Prokineticin 2 beta（PK2β）是趋化因子样蛋白。虽然PK2通过两个同源的G蛋白偶联受体，促动素受体1（PKR1）和促动素受体2（PKR2）以相同的效率进行信号传递来介导其生物学活性，但PK2β能够特异性结合PKR1。

趋化因子受体的细胞外环2（ECL2）是跨膜（TM）配体结合位点的一部分。在PKR2的ECL2中以及所有趋化因子受体中均存在一个芳香族残基簇，其中色氨酸212位于一个ECL2保守的半胱氨酸之后定位了四个残基，而苯丙氨酸198位于TM 4的顶部。

在这项工作中，通过琥珀色密码子抑制技术将可光活化的非天然氨基酸对苯甲酰基-L-苯丙氨酸掺入212位的PKR2中。可光活化交联的实验表明，色氨酸在212位对结合与色氨酸接触的配体的作用。第24位。我们还分析了苯丙氨酸198在PKR结合特异性中的作用。比较PKR1和PKR2之间的TM束结合位点，发现它们完全保守，除了一个残基：人PKR1中的缬氨酸207，其为人PKR2中的苯丙氨酸198。PKR2中的F198V突变允许获得能够更有效地结合PK2β（对PKR1高度特异的配体）的受体。