Evolution of antiparallel two-domain membrane proteins. Swapping domains in the glutamate transporter GltS

Two-domain membrane proteins are believed to have evolved through duplication and fusion events. A set of evolutionary states of the Na(+)-glutamate transporter of Escherichia coli was engineered. The two half-genes encoding the two domains were placed in a single operon in both orders (GltS(split)), and the split genes were fused in the reverse order compared to the original protein (GltS(swap)). The transporter halves were produced and shown to be active in Na(+)-coupled glutamate transport. GltS(swap) was as active as the original transporter provided that the domains were connected by a linker of the same size that connected them in the original transporter.