Identification of ligands for orphan G-protein-coupled receptors by using human immunodeficiency virus

(1)We已经显示四种G蛋白偶联受体，GPR 1、RDC 1、D 6和FML 1，作为HIV-1感染的共受体起作用。其中，已知RDC 1和GPR 1是孤儿受体，即它们的配体尚未被鉴定。GPR 1的氨基酸序列与趋化因子受体的氨基酸序列几乎没有相似性。因此，为了推断其配体，我们制作了GPCR的系统发育树，这些GPCR被认为是由数百种不同类型组成的，使用它们在从人类基因组计划确定的核苷酸序列中推导出的氨基酸序列中的相似性。趋化因子受体由CCR或CXCR趋化因子的受体组成，形成该树的单个分支。GPR 1与另一种孤儿趋化因子受体DEZ最相似，也与FML 1非常相似。据报道，FML 1是来源于细菌来源的消化产物的寡肽的受体。因此，GPR 1也可能作为外源寡肽的受体发挥作用。(2)We已经表明，衍生自爱帕琳的肽抑制表达爱帕琳受体APJ的HIV-1 tpNP-2细胞的感染。接下来，我们测试了是否有可能筛选肽作为孤儿GPCR配体的概率，特别是GPR 1和RDC 1。合成GPR 1、CCR 5或CXCR 4的N-末端肽，并检测其抑制HIV-1感染表达GPR 1、CCR 5或CXCR 4作为共受体的NP-2细胞的能力。由27个氨基酸组成的GPR 1的N-末端肽（但CCR 5或CXR 4的N-末端肽）抑制HIV-1、HIV-2或SIV对不仅表达GPR 1而且表达CCR 5或CXCR 4的NP-2细胞的感染。用HIV-1或HIV-2感染的NP-2/CD 4细胞系统将适合于筛选孤儿GPCR的配体。(3)We已经筛选了100多种从大坂蛋白质研究所获得的寡肽。不幸的是，没有一种肽明显抑制HIV-1或HIV-2感染。

(1)We have shown four G-protein-coupled receptors, GPR1,RDC1,D6 and FML1, function as co-receptors for HIV-1 infection. Among them, RDC1 and GPR1 are known to be orphan receptors, namely, their ligands have not been identified yet. The amino acid sequence of GPR1 shows little similarities to those of chemokine receptors. Therefore, to infer its ligand, we made a phylogenetic tree of GPCRs, which have been thought to be consisting of several hundred different types, using their similarities in their amino acid sequences deduced from their nucleotide sequences determined upon the Human Genome Projects. Chemokine receptors, consisting of receptors for CCR or CXCR chemokines, formed a single branch of the tree. GPR1 was the most similar to another orphan chemokine receptor, DEZ, and was also markedly similar to FML1. FML1 has been reported to be a receptor for oligoneptides derived from digested products of bacterial origins. Therefore, there is a possibility that GPR1 is also functioning as a receptor for exogenous oligoneptides.(2)We have shown that the peptides derived from apelin inhibit infection of HIV-1 tpNP-2 cell expressing APJ, a receptor for apelin. Next we tested whether it is possible to screen peptides for their probabilities as a ligand for orphan GPCRs, especially GPR1 and RDC1. The N-terminal peptides of GPR1, CCR5 or CXCR4 were synthesized and examined for abilities to inhibit HIV-1 infection to NP-2 cells expressing GPR1,CCR5 or CXCR4 as a co-receptor. Only the N-terminal peptide of GPR1 but CCR5 or CXR4, consisting of 27 amino acids, inhibited infection of NP-2 cells expressing not only GPR1 but also CCR5 or CXCR4 with HIV-1,HIV-2 or SIV. The NP-2/CD4 cell system to be infected with HIV-1 or HIV-2 will be suitable for screening of ligands for orphan GPCRs.(3)We have screened more than 100 oligopeptides obtained from the Protein Research Institute, Osaka. Unfortunately, none of the peptides markedly inhibited HIV-1 or HIV-2 infection.