Functional Characterization of Centrally Expressed Solute Carriers and G Protein-Coupled Receptors

Sammanfattning: Transmembrane proteins are gatekeepers of the cells; controlling the transport of substrates as well as communicating signals among cells and between the organelles and cytosol. Solute carriers (SLC) and G protein-coupled receptors (GPCR) are the largest family of membrane transporters and membrane receptors respectively. The overall aim of this thesis was to provide a basic understanding of some of the novel SLCs and GPCRs with emphasis on expression, transport property, evolution and probable function.The first part of the thesis directs towards the study of some novel solute carriers. In an initial study, we provided an overall picture of the sequence relationship and tissue expression of 14 diverse atypical SLCs confirming some of their evolutionary conservation and highly specific expression pattern. The focus then was on the SLC17 family (mainly vesicular proteins) and a novel member named Slc17a9. This study revealed that SLC17 family could be divided into four main phylogenetic clades which were all present before the divergence of the insect lineage with Slc17a9 having the most restricted evolutionary history. Detailed expression study of Slc17a9 in the mouse brain suggests that it is also expressed in some regions important for purinergic neurotransmission. Further, we deorphanised an aminoacid transporter Slc38a7 which was expressed in a majority of neurons in the CNS and showed that it preferably mediate transport of L–glutamine and L–histidine.The second part of the thesis focuses on the study of two GPCRs belonging to the Rhodopsin superfamily, Gpr162 and Gpr153. A phylogenetic analysis revealed that both Gpr153 and Gpr162 originated from a common ancestor before the radiation of the mammalian lineage. Expression study revealed that Gpr162 had a predominant expression in the CNS and relatively lower expression in the other tissue tested whereas Gpr153 had a more widespread and similar expression pattern in both CNS and peripheral tissues. The functional studies of the two GPCRs were done using the antisense oligodeoxynucleotide knockdown rat model. These studies provided evidence linking the orphan Gpr162 gene with the regulation of food intake– related behaviour whereas Gpr153 gene caused only a slight reduction in food intake.