SecD and SecF are prokaryotic protein export
membrane proteins
Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...
. They are a part of the larger multimeric protein export
complex comprising
SecA, D, E, F, G, Y, and YajC.
SecD and SecF are required to maintain a
proton motive force.
Secretion 440px
Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical ...
across the inner
membrane in some Gram-negative
bacteria occurs via the preprotein translocase pathway.
Proteins
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
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, including a
chaperone protein (SecB), an ATPase (SecA), an integral
membrane complex (SecCY, SecE and SecG), and two additional
membrane proteins that promote the release of the mature
peptide into the periplasm (SecD and SecF).
The
chaperone protein SecB
is a highly
acidic homotetrameric protein that exists as a "dimer of dimers" in the
bacterial cytoplasm. SecB maintains preproteins in an unfolded state after translation, and targets these to the
peripheral
A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...
membrane protein ATPase SecA for secretion.
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. The
structure
A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...
of the ''Escherichia coli'' SecYEG assembly revealed a sandwich of two
membranes interacting through the extensive cytoplasmic
domains.
Each
membrane is composed of
dimers of SecYEG. The monomeric complex contains 15
transmembrane helices.
This family consists of various
prokaryotic SecD and SecF protein export
membrane proteins. The SecD and SecF equivalents of the
Gram-positive bacterium ''Bacillus subtilis'' are jointly present in one polypeptide, denoted SecDF, that is required to maintain a high capacity for protein secretion. Unlike the SecD subunit of the pre-protein translocase of E. coli, SecDF of B. subtilis was not required for the release of a mature secretory protein from the membrane, indicating that SecDF is involved in earlier
translocation
Translocation may refer to:
* Chromosomal translocation, a chromosome abnormality caused by rearrangement of parts
** Robertsonian translocation, a chromosomal rearrangement in pairs 13, 14, 15, 21, and 22
** Nonreciprocal translocation, transfer ...
steps.
Comparison with SecD and SecF proteins from other
organisms revealed the presence of 10 conserved regions in SecDF, some of which appear to be important for SecDF function. The SecDF protein of B. subtilis has 12 putative transmembrane
domains. Thus, SecDF does not only show
sequence similarity but also structural similarity to secondary
solute transporter
Transporter may refer to:
* Transporter (vehicles), types of vehicles designed to transport items
* Transporter wagon, a railway car designed to carry another railway car
* Volkswagen Transporter, a model of van
* Transporter bridge, a bridge wh ...
s.
References
{{InterPro content, IPR022645
Protein families
Secretion