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Mitochondrial protein translocase (MPT) (Chacinska et al., 2005; Mokranjac et al., 2005; Bihlmaier et al., 2007). The crystal structure of the intermembrane space domain of yeast Tim50 has been solved to 1.83 Å resolution (Qian et al., 2011). A protruding beta-hairpin of Tim50 is crucial for interaction with Tim23, providing a molecular basis for the cooperation of Tim50 and Tim23 in preprotein translocation to the protein-conducting channel of the mitochondrial inner membrane (Qian et al., 2011).  TIM23-mediates insertion of transmembrane α-helices into the mitochondrial inner membrane (Botelho et al., 2011). The TIM23 channel undergoes structural changes in response to the energized state of the membrane, the pmf (Malhotra et al. 2013).  TMS1 in TIM23 is required for homodimerization while it and TMS2 are involved in pre-protein binding in the channel (Pareek et al. 2013).  The Tom40 outer membrane channel may be a 19 β-stranded barrel, possibly homologous to the VDAC porins (TC# 1.B.8) (Lackey et al. 2014).  Tim23 and Tim17 interact with each other as well as Tim44 and Pam17, respectively.  These last two proteins may serve regulatory functions (Ting et al. 2014).  Tom20, 22, 40 and 70 recognize presequences in various mitochondrially targetted proteins (Melin et al. 2015; Melin et al. 2014).  In the 4 TMS TIM17 protein, mutations in TMSs1 and 2 impair the interaction of Tim17 with Tim23, whereas mutations in TM3 compromise binding of the import motor (Demishtein-Zohary et al. 2017); further, residues in the matrix-facing region of Tim17 involved in binding of the import motor were identified. TIM22, forms an intramolecular disulfide bond in yeast and humans.  If not oxidized, they do not properly integrate into the membrane complex, and the lack of Tim17 oxidation disrupts the TIM23 translocase complex (Wrobel et al. 2016). Mgr2 (TC# 1.A.111.1.3) and Pam18 are involved in precursormembrane protein quality control (Schendzielorz et al. 2018). Tom7 and OMA1 play reciprocal roles during mitochondrial import and activation of the PTEN-induced kinase 1, PINK1, in humans (Sekine et al. 2019).  Organellar beta-barrel proteins are unique as most of them do not contain typical targeting information in the form of an N-terminal cleavable targeting signal. Instead, targeting and surface recognition of mitochondrial beta-barrel proteins in yeast, humans and plants depends on the hydrophobicity of the last beta-hairpin of the beta-barrel. Klinger et al. 2019 demonstrated that hydrophobicity is not sufficient for the discrimination of targeting to chloroplasts or mitochondria. Using atVDAC1 (TC# 1.B.8.1.15) and psOEP24 (1.B.28.1.1) they showed that the presence of a hydrophilic amino acid at the C-terminus of the penultimate beta-strand is required for mitochondrial targeting. A mutation of the chloroplast beta-barrel protein psOEP24 which mimics such a profile is efficiently targeted to mitochondria (Klinger et al. 2019). The high-resolution cryo-EM structures of the core TOM complex from Saccharomyces cerevisiae in dimeric and tetrameric forms have  been determined (Tucker and Park 2019). Dimeric TOM consists of two copies each of five proteins arranged in two-fold symmetry: pore-forming beta-barrel protein Tom40 and four auxiliary alpha-helical transmembrane proteins. The pore of each Tom40 has an overall negatively charged inner surface due to multiple functionally important acidic patches. The tetrameric complex is a dimer of dimeric TOM, which may be capable of forming higher-order oligomers. Negatively charged residues in the N-terminus of Tim17 are critical for the preprotein-induced gating of the TIM23 translocase, possibly by recognizing the positive charges in the leader sequence of the substrate proteins (Meier et al. 2005).  

Accession Number:P42834
Protein Name:Mdj2 aka YNL328C
Molecular Weight:16474.00
Species:Saccharomyces cerevisiae (Baker's yeast) [4932]
Number of TMSs:1
Location1 / Topology2 / Orientation3: Mitochondrion inner membrane1
Substrate proteins

Cross database links:

Genevestigator: P42834
eggNOG: fuNOG11793
DIP: DIP-4690N
RefSeq: NP_014071.1   
Entrez Gene ID: 855388   
Pfam: PF00226   
KEGG: sce:YNL328C   

Gene Ontology

GO:0001405 C:presequence translocase-associated import m...
GO:0001671 F:ATPase activator activity
GO:0031072 F:heat shock protein binding
GO:0030150 P:protein import into mitochondrial matrix
GO:0006950 P:response to stress

References (7)

[1] “Sequencing analysis of a 15.4 kb fragment of yeast chromosome XIV identifies the RPD3, PAS8 and KRE1 loci, five new open reading frames.”  Maftahi   7645347
[2] “The nucleotide sequence of Saccharomyces cerevisiae chromosome XIV and its evolutionary implications.”  Philippsen   9169873
[3] “Approaching a complete repository of sequence-verified protein-encoding clones for Saccharomyces cerevisiae.”  Hu   17322287
[4] “Mdj2p, a novel DnaJ homolog in the mitochondrial inner membrane of the yeast Saccharomyces cerevisiae.”  Westermann   9325105
[5] “Global analysis of protein localization in budding yeast.”  Huh   14562095
[6] “Global analysis of protein expression in yeast.”  Ghaemmaghami   14562106
[7] “The import motor of the yeast mitochondrial TIM23 preprotein translocase contains two different J proteins, Tim14 and Mdj2.”  Mokranjac   16027163

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