31 research outputs found
SecA mediated protein translocation in Escherichia coli
No full textThe movement of proteins across or integration of proteins into the cytoplasmic membrane of Escherichia coli is mediated by the multimeric membrane protein complex translocase. The core of the translocase consists of a motor protein, the ATPase SecA, and a protein-conducting channel, formed by the integral membrane proteins SecY and SecE. The SecYE complex is highly conserved, with homologs in the cytoplasmic membrane of Archae, the chloroplast thylakoid membrane, and the eukaryotic endoplasmatic reticulum (ER). SecA is unique for the bacterial post-translational translocation pathway. It is absent both in Archaea and in the eukaryotic ER, but a homolog exists in plant chloroplasts. SecA is an soluble protein that distributes between cytoplasmic and membrane associated states. The interaction with the cytoplasmic membrane occurs via low affinity interactions with anionic phospholipids and by a high affinity interaction with the SecYEG complex. At the membrane SecA forms a receptor for preproteins and drives their stepwise movement through the SecYEG channel [93, 173]. ...
Zie: Summary.
Arginine 357 of SecY is needed for SecA-dependent initiation of preprotein translocation
No full textThe Escherichia coli SecYEG complex forms a transmembrane channel for both protein export and membrane protein insertion. Secretory proteins and large periplasmic domains of membrane proteins require for translocation in addition the SecA ATPase. The conserved arginine 357 of SecY is essential for a yet unidentified step in the SecA catalytic cycle. To further dissect its role, we have analysed the requirement for R357 in membrane protein insertion. Although R357 substitutions abolish post-translational translocation, they allow the translocation of periplasmic domains targeted co-translationally by an N-terminal transmembrane segment. We propose that R357 is essential for the initiation of SecA-dependent translocation only.
The YidC/Oxa1/Alb3 protein family: common principles and distinct features
No full textThe members of the YidC/Oxa1/Alb3 protein family are evolutionary conserved in all three domains of life. They facilitate the insertion of membrane proteins into bacterial, mitochondrial, and thylakoid membranes and have been implicated in membrane protein folding and complex formation. The major classes of substrates are small hydrophobic subunits of large energy-transducing complexes involved in respiration and light capturing. All YidC-like proteins share a conserved membrane region, whereas the N- and C-terminal regions are diverse and fulfill accessory functions in protein targeting.
The F286Y mutation of PrlA4 tempers the signal sequence suppressor phenotype by reducing the SecA binding affinity
No full textSecYEG forms the protein-conducting channel of the Escherichia coli translocase. It binds the peripheral ATPase SecA that drives the preprotein translocation reaction. PrlA4 is a double mutant of SecY that enables the translocation of preproteins with a defective or even missing signal sequence. The effect of the individual mutations, F286Y and I408N, was studied with SecYEG proteoliposomes. SecY(I408N) is responsible for the increased translocation of preproteins with a defective and normal signal sequence, and exhibits a stronger prl phenotype than PrlA4. This activity correlates with an elevated SecA-translocation ATPase and SecA binding affinity. SecY(F286Y) supports only a low SecA binding affinity, preprotein translocation and SecA translocation ATPase activity. These results suggest that the second site F286Y mutation reduces the strength of the I408N mutation of PrlA4 by lowering the SecA binding affinity.
