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The role of Fis1p-Mdv1p interactions in mitochondrial fission complex assembly.

Karren MA, Coonrod EM, Anderson TK, Shaw JM - J. Cell Biol. (2005)

Bottom Line: Furthermore, we show that conditional mutations in the Fis1p TPR-like domain cause fission complex assembly defects that are suppressed by mutations in the Mdv1p-predicted coiled coil.We also define separable functions for the Fis1p NH(2)-terminal arm and TPR-like fold.These studies suggest that the concave binding surface of the Fis1p TPR-like fold interacts with Mdv1p during mitochondrial fission and that Mdv1p facilitates Dnm1p recruitment into functional fission complexes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, UT 84132, USA.

ABSTRACT
Mitochondrial division requires coordinated interactions among Fis1p, Mdv1p, and the Dnm1p GTPase, which assemble into fission complexes on the outer mitochondrial membrane. The integral outer membrane protein Fis1p contains a cytoplasmic domain consisting of a tetratricopeptide repeat (TPR)-like fold and a short NH(2)-terminal helix. Although it is known that the cytoplasmic domain is necessary for assembly of Mdv1p and Dnm1p into fission complexes, the molecular details of this assembly are not clear. In this study, we provide new evidence that the Fis1p-Mdv1p interaction is direct. Furthermore, we show that conditional mutations in the Fis1p TPR-like domain cause fission complex assembly defects that are suppressed by mutations in the Mdv1p-predicted coiled coil. We also define separable functions for the Fis1p NH(2)-terminal arm and TPR-like fold. These studies suggest that the concave binding surface of the Fis1p TPR-like fold interacts with Mdv1p during mitochondrial fission and that Mdv1p facilitates Dnm1p recruitment into functional fission complexes.

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Proposed pathway for mitochondrial fission complex assembly. (1) Before fission complex assembly, the NH2-terminal arm of yeast Fis1p (indicated) interacts with the TPR-like binding pocket (Suzuki et al., 2005). (2) Assembly begins when Mdv1p binds the Fis1p TPR-like binding pocket. The NH2-terminal arm facilitates this interaction but is not strictly required as previously proposed. (3) In the next step, the Fis1p–Mdv1p complex serves as an assembly platform for Dnm1p, which binds as a dimer or a preassembled oligomer. This differs from previous models, which propose that Dnm1p membrane recruitment is the first step in complex assembly. Cyt, cytoplasm; OM, mitochondrial outer membrane; IMS, inter membrane space.
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fig10: Proposed pathway for mitochondrial fission complex assembly. (1) Before fission complex assembly, the NH2-terminal arm of yeast Fis1p (indicated) interacts with the TPR-like binding pocket (Suzuki et al., 2005). (2) Assembly begins when Mdv1p binds the Fis1p TPR-like binding pocket. The NH2-terminal arm facilitates this interaction but is not strictly required as previously proposed. (3) In the next step, the Fis1p–Mdv1p complex serves as an assembly platform for Dnm1p, which binds as a dimer or a preassembled oligomer. This differs from previous models, which propose that Dnm1p membrane recruitment is the first step in complex assembly. Cyt, cytoplasm; OM, mitochondrial outer membrane; IMS, inter membrane space.

Mentions: Is the Mdv1p-binding site on yeast Fis1p formed by the NH2-terminal arm, the TPR-like domain, or both? It has been hypothesized that the TPR-like hydrophobic pocket is a binding surface for other fission complex proteins (Dohm et al., 2004; Suzuki et al., 2005). Three lines of evidence that are presented in this study support the idea that Mdv1p occupies the Fis1p TPR-like binding pocket, possibly by displacing the NH2-terminal arm (Fig. 10). First, mutations in the Fis1p TPR-like binding pocket are suppressed by mutations in Mdv1p. Second, overexpressed Mdv1p interacts with Fis115–155p, which lacks the NH2-terminal arm. Third, the Mdv1E250Gp suppressor interacts with Fis115–155p, even when expressed at low levels. Thus, the TPR-like domain alone interacts with Mdv1p, and this interaction is augmented by the Mdv1p E250G substitution. Although these studies establish that Mdv1p interacts with the TPR-like domain, the Fis1p NH2-terminal arm is clearly important. We propose that the Fis1p NH2-terminal arm facilitates recruitment and/or stabilization of Mdv1p during fission complex assembly.


The role of Fis1p-Mdv1p interactions in mitochondrial fission complex assembly.

Karren MA, Coonrod EM, Anderson TK, Shaw JM - J. Cell Biol. (2005)

Proposed pathway for mitochondrial fission complex assembly. (1) Before fission complex assembly, the NH2-terminal arm of yeast Fis1p (indicated) interacts with the TPR-like binding pocket (Suzuki et al., 2005). (2) Assembly begins when Mdv1p binds the Fis1p TPR-like binding pocket. The NH2-terminal arm facilitates this interaction but is not strictly required as previously proposed. (3) In the next step, the Fis1p–Mdv1p complex serves as an assembly platform for Dnm1p, which binds as a dimer or a preassembled oligomer. This differs from previous models, which propose that Dnm1p membrane recruitment is the first step in complex assembly. Cyt, cytoplasm; OM, mitochondrial outer membrane; IMS, inter membrane space.
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Related In: Results  -  Collection

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fig10: Proposed pathway for mitochondrial fission complex assembly. (1) Before fission complex assembly, the NH2-terminal arm of yeast Fis1p (indicated) interacts with the TPR-like binding pocket (Suzuki et al., 2005). (2) Assembly begins when Mdv1p binds the Fis1p TPR-like binding pocket. The NH2-terminal arm facilitates this interaction but is not strictly required as previously proposed. (3) In the next step, the Fis1p–Mdv1p complex serves as an assembly platform for Dnm1p, which binds as a dimer or a preassembled oligomer. This differs from previous models, which propose that Dnm1p membrane recruitment is the first step in complex assembly. Cyt, cytoplasm; OM, mitochondrial outer membrane; IMS, inter membrane space.
Mentions: Is the Mdv1p-binding site on yeast Fis1p formed by the NH2-terminal arm, the TPR-like domain, or both? It has been hypothesized that the TPR-like hydrophobic pocket is a binding surface for other fission complex proteins (Dohm et al., 2004; Suzuki et al., 2005). Three lines of evidence that are presented in this study support the idea that Mdv1p occupies the Fis1p TPR-like binding pocket, possibly by displacing the NH2-terminal arm (Fig. 10). First, mutations in the Fis1p TPR-like binding pocket are suppressed by mutations in Mdv1p. Second, overexpressed Mdv1p interacts with Fis115–155p, which lacks the NH2-terminal arm. Third, the Mdv1E250Gp suppressor interacts with Fis115–155p, even when expressed at low levels. Thus, the TPR-like domain alone interacts with Mdv1p, and this interaction is augmented by the Mdv1p E250G substitution. Although these studies establish that Mdv1p interacts with the TPR-like domain, the Fis1p NH2-terminal arm is clearly important. We propose that the Fis1p NH2-terminal arm facilitates recruitment and/or stabilization of Mdv1p during fission complex assembly.

Bottom Line: Furthermore, we show that conditional mutations in the Fis1p TPR-like domain cause fission complex assembly defects that are suppressed by mutations in the Mdv1p-predicted coiled coil.We also define separable functions for the Fis1p NH(2)-terminal arm and TPR-like fold.These studies suggest that the concave binding surface of the Fis1p TPR-like fold interacts with Mdv1p during mitochondrial fission and that Mdv1p facilitates Dnm1p recruitment into functional fission complexes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, UT 84132, USA.

ABSTRACT
Mitochondrial division requires coordinated interactions among Fis1p, Mdv1p, and the Dnm1p GTPase, which assemble into fission complexes on the outer mitochondrial membrane. The integral outer membrane protein Fis1p contains a cytoplasmic domain consisting of a tetratricopeptide repeat (TPR)-like fold and a short NH(2)-terminal helix. Although it is known that the cytoplasmic domain is necessary for assembly of Mdv1p and Dnm1p into fission complexes, the molecular details of this assembly are not clear. In this study, we provide new evidence that the Fis1p-Mdv1p interaction is direct. Furthermore, we show that conditional mutations in the Fis1p TPR-like domain cause fission complex assembly defects that are suppressed by mutations in the Mdv1p-predicted coiled coil. We also define separable functions for the Fis1p NH(2)-terminal arm and TPR-like fold. These studies suggest that the concave binding surface of the Fis1p TPR-like fold interacts with Mdv1p during mitochondrial fission and that Mdv1p facilitates Dnm1p recruitment into functional fission complexes.

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