1. BIEKER, K.L., PHILLIPS, G.J. AND SILHAVY, T.J.
The sec and prl genes of Esherichia coli.
J.BIOENERG.BIOMEMBR. 22 291-310 (1990).
2. DRIESSEN, A.J., FEKKES, P. AND VAN DER WOLK, J.P.
The Sec system.
CURR.OPIN.MICROBIOL. 1 216-222 (1998).
3. DOUVILLE, K., PRICE, A., EICHLER, J., ECONOMOU, A. AND WICKNER, W.
SecYEG and SecA are the stoichiometric components of preprotein translocase.
J.BIOL.CHEM. 270 20106-20111 (1995).
4. VEENENDAAL, A.K., VAN DER DOES, C. AND DRIESSEN, A.J.
Mapping the sites of interaction between SecY and SecE by cysteine scanning
J.BIOL.CHEM. 276 32559-32566 (2001).
Secretion across the inner membrane in some Gram-negative bacteria occurs
via the preprotein translocase pathway. Proteins are produced in the
cytoplasm as precursors, and require a chaperone subunit to direct them to
the translocase component. . From there, the mature proteins are either
targeted to the outer membrane, or remain as periplasmic proteins . The
translocase protein subunits are encoded on the bacterial chromosome.
The translocase itself comprises 7 proteins, and consists of a chaperone
(SecB), an ATPase (SecA), an integral membrane complex (SecY, SecE and SecG),
and two additional membrane proteins that promote the release of the mature
peptide into the periplasm (SecD and SecF) . SecE, part of the main
SecYEG translocase complex, is ~106 residues in length, and spans the
inner membrane of the Gram-negative bacterial envelope . Together with
SecY and SecG, SecE forms a multimeric channel through which preproteins
are translocated, using both proton motive forces and ATP-driven secretion
. The latter is mediated by SecA.
Recently, using cysteine scanning mutatgenesis, it has been found that the
seventh transmembrane (TM) segment of SecY interacts with the third TM
segment of SecE . This alpha-helical cross-linking shows that SecY and
SecE exist in a 1:1 stoichiometry in the complex. The SecE protein itself
remains unaltered during preprotein insertion into the translocase pore,
retaining its tertiary structure .
SECETRNLCASE is a 4-element fingerprint that provides a signature for the
bacterial translocase SecE family. The fingerprint was derived from an
initial alignment of 4 sequences: the motifs were drawn from conserved
regions spanning the C-terminal portion of the alignment - motif 1 encodes
putative TM domain 2; motif 2 spans the following cytoplasmic loop; motif 3
encodes putative TM domain 3; and motif 4 resides at the periplasmic
C-terminus. Two iterations on SPTR40_18f were required to reach convergence,
at which point a true set comprising 7 sequences was identified. A single
partial match was also found, Q9HWC3, a Pseudomonas aeruginosa SecE
homologue that fails to make a significant match with motif 4.