THE TRANSLOCATION OF NEGATIVELY CHARGED RESIDUES ACROSS THE MEMBRANE IS DRIVEN BY THE ELECTROCHEMICAL POTENTIAL - EVIDENCE FOR AN ELECTROPHORESIS-LIKE MEMBRANE TRANSFER MECHANISM

The role of the membrane electrochemical potential in the translocatio n of acidic and basic residues across the membrane was investigated wi th the M13 procoat protein, which has a short periplasmic loop, and le ader peptidase, which has an extended periplasmically located N-termin al tail. For both proteins we find that the membrane potential promote s membrane transfer only when negatively charged residues are present within the translocated domain. When these residues are substituted by uncharged amino acids, the proteins insert into the membrane independ ently of the potential. In contrast, when a positively charged residue is present within the N-terminal tail of leader peptidase, the potent ial impedes translocation of the tail domain. However, an impediment w as not observed in the case of the procoat protein, where positively c harged residues in the central loop are translocated even in the prese nce of the membrane potential. Intriguingly, several of the negatively charged procoat proteins required the SecA and SecY proteins for opti mal translocation. The studies reported here provide insights into the role of the potential in membrane protein assembly and suggest that e lectrophoresis can play an important role in controlling membrane topo logy.