CARBOXYL-TERMINUS OF THE GLYCINE TRANSPORTER GLYT1 IS NECESSARY FOR CORRECT PROCESSING OF THE PROTEIN

The high affinity glycine transporter in neurons and glial cells is th e primary means of inactivating synaptic glycine. To understand the st ructure-function relationships, especially the role of the intracellul ar carboxyl- and amino-terminal domains, we have modified the glycine transporter GLYT1 by using a polymerase chain reaction-based mutagenes is approach. Deletion of the first 30 amino acids of the amino terminu s does not alter transport of glycine. Truncation of the last 34 amino acids of the carboxyl terminus did not impair glycine transport, but progressively more extensive deletions produced a progressive decrease in transport activity. AU the fully active or partially active forms of the transporter retain the characteristic sodium and chloride depen dence of the wild type. When the nonfunctional mutants of the carboxyl terminus were examined by an immunofluorescence technique, the carrie r was no longer found in the membrane. This suggests that the carboxyl terminus of GLYT1 may be involved in the membrane insertion process. Moreover, the transporter that is not fully processed is not functiona l, because transport activity cannot be rescued in a solubilization-re constitution experiment.