scholarly journals Nucleotides and Substrates Trigger the Dynamics of the Toc34 GTPase Homodimer Involved in Chloroplast Preprotein Translocation

Structure ◽  
2014 ◽  
Vol 22 (4) ◽  
pp. 526-538 ◽  
Author(s):  
Christina Lumme ◽  
Hasret Altan-Martin ◽  
Reza Dastvan ◽  
Maik S. Sommer ◽  
Mislav Oreb ◽  
...  
Keyword(s):  
Preprotein Translocation

scholarly journals The essential yeast protein MIM44 (encoded by MPI1) is involved in an early step of preprotein translocation across the mitochondrial inner membrane.

1993 ◽  
Vol 13 (12) ◽  
pp. 7364-7371 ◽  
Author(s):  
J Blom ◽  
M Kübrich ◽  
J Rassow ◽  
W Voos ◽  
P J Dekker ◽  
...  
Keyword(s):  
Protein Import ◽  
Early Stage ◽  
Proteolytic Processing ◽  
Early Step ◽  
Direct Role ◽  
Inner Membrane ◽  
Mitochondrial Inner Membrane ◽  
Preprotein Translocation ◽  
In Transit

The essential yeast gene MPI1 encodes a mitochondrial membrane protein that is possibly involved in protein import into the organelle (A. C. Maarse, J. Blom, L. A. Grivell, and M. Meijer, EMBO J. 11:3619-3628, 1992). For this report, we determined the submitochondrial location of the MPI1 gene product and investigated whether it plays a direct role in the translocation of preproteins. By fractionation of mitochondria, the mature protein of 44 kDa was localized to the mitochondrial inner membrane and therefore termed MIM44. Import of the precursor of MIM44 required a membrane potential across the inner membrane and involved proteolytic processing of the precursor. A preprotein in transit across the mitochondrial membranes was cross-linked to MIM44, whereas preproteins arrested on the mitochondrial surface or fully imported proteins were not cross-linked. When preproteins were arrested at two distinct stages of translocation across the inner membrane, only preproteins at an early stage of translocation could be cross-linked to MIM44. Moreover, solubilized MIM44 was found to interact with in vitro-synthesized preproteins. We conclude that MIM44 is a component of the mitochondrial inner membrane import machinery and interacts with preproteins in an early step of translocation.

Glycolipozyme membrane protein integrase (MPIase): recent data

2014 ◽  
Vol 5 (5) ◽  
pp. 429-438 ◽  
Author(s):  
Ken-ichi Nishiyama ◽  
Keiko Shimamoto
Keyword(s):  
Escherichia Coli ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Structure Determination ◽  
Molecular Chaperone ◽  
Molecular Mechanisms ◽  
Cytoplasmic Membrane ◽  
Amino Sugars ◽  
Glycan Chain ◽  
Preprotein Translocation

AbstractA novel factor for membrane protein integration, from the cytoplasmic membrane of Escherichia coli, named MPIase (membrane protein integrase), has recently been identified and characterized. MPIase was revealed to be essential for the membrane integration of a subset of membrane proteins, despite that such integration reactions have been, thus far, thought to occur spontaneously. The structure determination study revealed that MPIase is a novel glycolipid comprising a glycan chain with three N-acetylated amino sugars connected to diacylglycerol through a pyrophosphate linker. As MPIase catalyzes membrane protein integration, we propose that MPIase is a glycolipozyme on the basis of its enzyme-like function. The glycan chain exhibits a molecular chaperone-like function by directly interacting with substrate membrane proteins. Moreover, MPIase also affects the dimer structure of SecYEG, a translocon, thereby significantly stimulating preprotein translocation. The molecular mechanisms of MPIase functions will be outlined.

scholarly journals Sec-dependent preprotein translocation in bacteria

1996 ◽  
Vol 165 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Tanneke den Blaauwen ◽  
A. J. M. Driessen
Keyword(s):  
Preprotein Translocation

scholarly journals Toc64, a New Component of the Protein Translocon of Chloroplasts

2000 ◽  
Vol 148 (6) ◽  
pp. 1213-1222 ◽  
Author(s):  
Karen Sohrt ◽  
Jürgen Soll
Keyword(s):  
Protein Import ◽  
Disulfide Bridge ◽  
Tetratricopeptide Repeat ◽  
Outer Envelope ◽  
High Molecular Weight Complex ◽  
A Subunit ◽  
Reversible Formation ◽  
Preprotein Translocation ◽  
Envelope Membranes ◽  
Docking Protein

A subunit of the preprotein translocon of the outer envelope of chloroplasts (Toc complex) of 64 kD is described, Toc64. Toc64 copurifies on sucrose density gradients with the isolated Toc complex. Furthermore, it can be cross-linked in intact chloroplasts to a high molecular weight complex containing both Toc and Tic subunits and a precursor protein. The 0 Å cross-linker CuCl2 yields the reversible formation of disulfide bridge(s) between Toc64 and the established Toc complex subunits in purified outer envelope membranes. Toc64 contains three tetratricopeptide repeat motifs that are exposed at the chloroplast cytosol interface. We propose that Toc64 functions early in preprotein translocation, maybe as a docking protein for cytosolic cofactors of the protein import into chloroplasts.

scholarly journals The targeting of the atToc159 preprotein receptor to the chloroplast outer membrane is mediated by its GTPase domain and is regulated by GTP

2002 ◽  
Vol 159 (5) ◽  
pp. 833-843 ◽  
Author(s):  
Matthew D. Smith ◽  
Andreas Hiltbrunner ◽  
Felix Kessler ◽  
Danny J. Schnell
Keyword(s):  
Envelope Membrane ◽  
Outer Envelope ◽  
Gtpase Domain ◽  
Gtp Hydrolysis ◽  
Gtp Binding ◽  
Direct Binding ◽  
Outer Envelope Membrane ◽  
Preprotein Translocation ◽  
Initial Binding ◽  
Intrinsic Gtpase Activity

The multimeric translocon at the outer envelope membrane of chloroplasts (Toc) initiates the recognition and import of nuclear-encoded preproteins into chloroplasts. Two Toc GTPases, Toc159 and Toc33/34, mediate preprotein recognition and regulate preprotein translocation. Although these two proteins account for the requirement of GTP hydrolysis for import, the functional significance of GTP binding and hydrolysis by either GTPase has not been defined. A recent study indicates that Toc159 is equally distributed between a soluble cytoplasmic form and a membrane-inserted form, raising the possibility that it might cycle between the cytoplasm and chloroplast as a soluble preprotein receptor. In the present study, we examined the mechanism of targeting and insertion of the Arabidopsis thaliana orthologue of Toc159, atToc159, to chloroplasts. Targeting of atToc159 to the outer envelope membrane is strictly dependent only on guanine nucleotides. Although GTP is not required for initial binding, the productive insertion and assembly of atToc159 into the Toc complex requires its intrinsic GTPase activity. Targeting is mediated by direct binding between the GTPase domain of atToc159 and the homologous GTPase domain of atToc33, the Arabidopsis Toc33/34 orthologue. Our findings demonstrate a role for the coordinate action of the Toc GTPases in assembly of the functional Toc complex at the chloroplast outer envelope membrane.

scholarly journals Pam17 Is Required for Architecture and Translocation Activity of the Mitochondrial Protein Import Motor

2005 ◽  
Vol 25 (17) ◽  
pp. 7449-7458 ◽  
Author(s):  
Martin van der Laan ◽  
Agnieszka Chacinska ◽  
Maria Lind ◽  
Inge Perschil ◽  
Albert Sickmann ◽  
...  
Keyword(s):  
Protein Import ◽  
Mitochondrial Protein ◽  
Matrix Proteins ◽  
Stable Complex ◽  
Nucleotide Exchange ◽  
Inner Membrane ◽  
Reading Frame ◽  
Nucleotide Exchange Factor ◽  
The Matrix ◽  
Preprotein Translocation

ABSTRACT Import of mitochondrial matrix proteins involves the general translocase of the outer membrane and the presequence translocase of the inner membrane. The presequence translocase-associated motor (PAM) drives the completion of preprotein translocation into the matrix. Five subunits of PAM are known: the preprotein-binding matrix heat shock protein 70 (mtHsp70), the nucleotide exchange factor Mge1, Tim44 that directs mtHsp70 to the inner membrane, and the membrane-bound complex of Pam16-Pam18 that regulates the ATPase activity of mtHsp70. We have identified a sixth motor subunit. Pam17 (encoded by the open reading frame YKR065c) is anchored in the inner membrane and exposed to the matrix. Mitochondria lacking Pam17 are selectively impaired in the import of matrix proteins and the generation of an import-driving activity of PAM. Pam17 is required for formation of a stable complex between the cochaperones Pam16 and Pam18 and promotes the association of Pam16-Pam18 with the presequence translocase. Our findings suggest that Pam17 is required for the correct organization of the Pam16-Pam18 complex and thus contributes to regulation of mtHsp70 activity at the inner membrane translocation site.

scholarly journals A single copy of SecYEG is sufficient for preprotein translocation

2011 ◽  
Vol 30 (21) ◽  
pp. 4387-4397 ◽  
Author(s):  
Alexej Kedrov ◽  
Ilja Kusters ◽  
Victor V Krasnikov ◽  
Arnold J M Driessen
Keyword(s):  
Single Copy ◽  
Preprotein Translocation
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