Title : Glycosyl modification facilitates homo- and hetero-oligomerization of the serotonin transporter
Abstract :
- A specific role for sialic acid residues.
- The serotonin transporter ( SERT ) is an oligomeric glycoprotein with two sialic acid residues on each of two complex oligosaccharide molecules
- In this study, we investigated the contribution of N-glycosyl modification to the structure and function of SERT in two model systems: wild-type SERT expressed in sialic acid-defective Lec4 Chinese hamster ovary (CHO) cells and a mutant form (after site-directed mutagenesis of Asn-208 and Asn-217 to Gln ) of SERT , QQ, expressed in parental CHO cells
- In both systems, SERT monomers required modification with both complex oligosaccharide residues to associate with each other and to function in homo-oligomeric forms
- However, defects in sialylated N-glycans did not alter surface expression of the SERT protein
- Furthermore, in heterologous (CHO and Lec4 cells) and endogenous (placental choriocarcinoma JAR cells) expression systems, we tested whether glycosyl modification also manipulates the hetero-oligomeric interactions of SERT , specifically with myosin IIA
- SERT is phosphorylated by cGMP-dependent protein kinase G kinase G through interactions with anchoring proteins , and myosin is a protein kinase G-anchoring protein
- A physical interaction between myosin and SERT was apparent; however, defects in sialylated N-glycans impaired association of SERT with myosin as well as the stimulation of the serotonin uptake function in the cGMP-dependent pathway
- We propose that sialylated N-glycans provide a favorable conformation to SERT that allows the transporter to function most efficiently via its protein- protein interactions