RESUMO
The SecE protein is an essential component of the SecAYE-translocase, which mediates protein translocation across the cytoplasmic membrane in bacteria. In the thylakoid membranes of chloroplasts, a protein homologous to SecE, chloroplastic (cp) SecE, has been identified. However, the functional role of cpSecE has not been established experimentally. In this report we show that cpSecE in cells depleted for bacterial SecE (i) supports growth, (ii) stabilizes, just like bacterial SecE, the Sec-translocase core component SecY, and (iii) supports Sec-dependent protein translocation. This indicates that cpSecE can functionally replace bacterial SecE in vivo, and strongly suggests that the thylakoid membrane contains a SecAYE-like translocase with functional and structural similarities to the bacterial complex. This study further underscores the evolutionary link between chloroplasts and bacteria.
Assuntos
Proteínas de Bactérias/metabolismo , Cloroplastos/metabolismo , Proteínas de Escherichia coli , Escherichia coli/metabolismo , Teste de Complementação Genética , Proteínas de Membrana Transportadoras , Adenosina Trifosfatases , Sequência de Aminoácidos , Arabidopsis/metabolismo , Proteínas de Bactérias/análise , Proteínas de Bactérias/genética , Proteínas de Transporte , Cloroplastos/genética , Escherichia coli/genética , Escherichia coli/crescimento & desenvolvimento , Dados de Sequência Molecular , Transporte Proteico , Canais de Translocação SEC , Proteínas SecA , Homologia de Sequência de AminoácidosRESUMO
Recent studies identified YidC as a novel membrane factor that may play a key role in membrane insertion of inner membrane proteins (IMPs), both in conjunction with the Sec-translocase and as a separate entity. Here, we show that the type II IMP FtsQ requires both the translocase and, to a lesser extent, YidC in vivo. Using photo-crosslinking we demonstrate that the transmembrane (TM) domain of the nascent IMP FtsQ inserts into the membrane close to SecY and lipids, and moves to a combined YidC/lipid environment upon elongation. These data are consistent with a crucial role for YidC in the lateral transfer of TM domains from the Sec translocase into the lipid bilayer.
