Export of Thermus thermophilus alkaline phosphatase via the twin-arginine translocation pathway in Escherichia coli

The bacterial twin-arginine translocation (Tat) pathway is distinct from the See system by its remarkable capacity to export folded enzymes. To address the question whether the two systems are capable of translocating homologous enzymes catalyzing the same reaction, we cloned the tap gene encoding Thermus thermophilus alkaline phosphatase (Tap) and expressed it in Escherichia coli. Unlike the alkaline phosphatase of E. coli, which is translocated through the See system and then activated in the periplasm, Tap was exported exclusively via the Tat pathway and active Tap precursor was observed in the cytoplasm. These results demonstrate that two sequence and functional related enzymes are exported by distinct protein transport systems, which may play an integral role in the bacterial adaptation to their environment during the evolution. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science BN. All rights reserved.