title: Characterization of Mmp37p, a Saccharomyces cerevisiae mitochondrial matrix protein with a role in mitochondrial protein import.
abstract: Many mitochondrial proteins are encoded by nuclear genes and after translation in the cytoplasm are imported via translocases in the outer and inner membranes, the TOM and TIM complexes, respectively. Here, we report the characterization of the mitochondrial protein, Mmp37p (YGR046w) and demonstrate its involvement in the process of protein import into mitochondria. Haploid cells deleted of MMP37 are viable but display a temperature-sensitive growth phenotype and are inviable in the absence of mitochondrial DNA. Mmp37p is located in the mitochondrial matrix where it is peripherally associated with the inner membrane. We show that Mmp37p has a role in the translocation of proteins across the mitochondrial inner membrane via the TIM23-PAM complex and further demonstrate that substrates containing a tightly folded domain in close proximity to their mitochondrial targeting sequences display a particular dependency on Mmp37p for mitochondrial import. Prior unfolding of the preprotein, or extension of the region between the targeting signal and the tightly folded domain, relieves their dependency for Mmp37p. Furthermore, evidence is presented to show that Mmp37 may affect the assembly state of the TIM23 complex. On the basis of these findings, we hypothesize that the presence of Mmp37p enhances the early stages of the TIM23 matrix import pathway to ensure engagement of incoming preproteins with the mtHsp70p/PAM complex, a step that is necessary to drive the unfolding and complete translocation of the preprotein into the matrix.
authors.affiliation: Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Gallas
authors.forename: Mary K
authors.initials: MK
authors.lastname: Dienhart
authors.forename: Rosemary A
authors.initials: RA
authors.lastname: Stuart
authors.forename: Roy M
authors.initials: RM
authors.lastname: Long
mesh_terms: D002470:Cell Survival; D018834:Chaperonin 60; D018833:Chaperonins / Q000378:metabolism; D004272:DNA, Mitochondrial / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D006238:Haploidy; D006360:Heat-Shock Proteins / Q000378:metabolism; D008540:Meiosis; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000378:metabolism*; D016366:Open Reading Frames / Q000235:genetics; D017510:Protein Folding; D011498:Protein Precursors / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
chemical_list: D018834:Chaperonin 60; D004272:DNA, Mitochondrial; D050956:HSP40 Heat-Shock Proteins; C504495:HSP60 protein, S cerevisiae; D006360:Heat-Shock Proteins; C087041:MDJ1 protein, S cerevisiae; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D011498:Protein Precursors; D029701:Saccharomyces cerevisiae Proteins; C514109:TAM41 protein, S cerevisiae; C083081:TIM23 protein, S cerevisiae; D018833:Chaperonins