Possible existence of quaternary structure in the high-affinity serotonin transport complex.
Deletion-mutants of the cloned mouse serotonin transporter (SERT) rendered dominant negative-mutant effects upon wild-type transporter activities in heterologous expression studies; such effects were transporter-selective and did not influence the activities of co-expressed neuronal GABA transporter. Heterologous expression of linear concatenates (up to four copies) of SERT further revealed discernable uptake activities for both transporter-dimer and -tetramer, but not for the trimer. Kinetic and pharmacological analyses revealed that the monomer, dimer, and tetramer manifested comparable transport Km and potencies for known serotonin uptake inhibitors; the tetramer was distinct from the others only in manifesting notably reduced transport Vmax. Surprisingly, equivalent cocaine congener-binding activities were observed for all concatenates, including the functionally inactive trimer. These findings collectively support the existence of quaternary structure in the active 5-HT transport complex; such structure is likely to be a critical determinant of ligand transport activities, but apparently not of transporter-inhibitor interactions.
Chang
A S
AS
The Center for Biotechnology, Baylor College of Medicine, 4000 Research Forest Drive, The Woodlands, Texas, 77381, USA. asc6@po.cwru.edu
Starnes
D M
DM
Chang
S M
SM
D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003042:Cocaine / Q000378:metabolism; D019281:Dimerization; D017353:Gene Deletion; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D051379:Mice; D016296:Mutagenesis; D009419:Nerve Tissue Proteins; D011487:Protein Conformation; D012701:Serotonin / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors / Q000378:metabolism; D013329:Structure-Activity Relationship; D014162:Transfection
D002352:Carrier Proteins; D003042:Cocaine; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D012701:Serotonin; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors; C493231:Slc6a4 protein, mouse