코카인 결합과 관련된 도파민 수송체의 아미노산 구조

Amino Acid Structure of Dopamine Transporter Resonsible for Cocaine Binding

Human and bovine dopamine transporters (DAT) demonstrate discrete functional differences in the dopamine (DA) transport and cocaine binding. The functional analyses on the chimeras of human and bovine DAT have revealed that the region from the 133rd to 186th residue (encompassing the 3rd transmembrane domain(TM)) is responsible for the substrate transport and cocaine binding. The present studies have been done to find out the specific amino acid(s) which is essential for the binding of cocaine to DAT by interchanging the amino acids in that region between human and bovine DAT. When isoleucine, the 152nd residue of chimera B3 (bovine DAT sequence), was transformed back to valine, the human DAT residue at the identical position, the cocaine binding was remarkably recovered to 98% of the human DAT values. In addition, the cocaine binding of the human DAT was decreased by 57% by substituting isoleucine for valine at position 152. When isoleucine at position 152. When isoleucine at position 152 of the chimera B3 was converted to the other amino acids to provide an possible molecular basis for the functional role of the 152nd residue, only the conversion to alanine among the amino acids tested significantly increased the cocaine binding by 34%, but these effects were not as much as those by the conversion to valine. In conclusion, valine at position 152 is a crucial amino acid for the interaction of cocaine to the DAT.