ROSEMARY A. STUART 
Professor

B.Sc. 1984, University College, Dublin, Ireland
M.Sc. 1985, University College, Dublin, Ireland
Dr. rer. nat. 1989, Ludwig-Maximillians Universität, München, Germany
Postdoctoral position: Imperial Cancer Research Fund, London, U.K.
Dr. rer. biol. hum. Habil. 1998, Ludwig-Maximillians Universität, München, Germany

WLS 309
(414) 288-1472
e-mail: rosemary.stuart@marquette.edu

Mitochondrial Biogenesis using yeast as a model organism

Our research is focused on understanding the process of assembly of the mitochondrial respiratory chain complexes. We are using the yeast Saccharomyces cerevisiae as a model system and are adopting a variety of genetic and biochemical approaches. The mitochondrial respiratory chain is composed of a number of large multi-subunit complexes that are embedded in the inner mitochondrial membrane. The majority of proteins is encoded in the cell’s nucleus and is imported into the mitochondria. A few of the subunits of respiratory chain complexes are encoded by the mitochondrial genome and are synthesized within the matrix compartment. Our current research is focused on two aspects of the assembly process, (i) the sorting of mitochondrially encoded proteins into the inner membrane by a process which is mediated by the Oxa1p protein complex; and (ii) the assembly and function of the supercomplex assembly states of the mitochondrial oxidative phosphorylation machinery

The Oxa1p complex and its interaction with mitoribosomes

The mitochondrial Oxa1 protein is a member of the conserved Alb3/Oxa1/YidC protein family involved in the insertion of proteins into biological membranes throughout prokaryotes and eukaryotes. The presence of Oxa1 is required for the insertion of a subset of nuclearly- and mitochondrially-encoded proteins, coming from the mitochondrial matrix and integrating into the inner membrane. The mitochondrially encoded COX subunits, Cox1 and Cox2 in particular, are strongly dependent on Oxa1 for their insertion. A direct role for Oxa1 in the membrane insertion process was suggested by the demonstration that Oxa1 physically interacts with the COX subunits during their synthesis as nascent polypeptide chains, i.e. in a co-translational fashion. We have recently provided evidence for a direct physical interaction between Oxa1 and the mitoribosome and propose that this close association ensures a tight coupling the translation and membrane insertion events. We propose to further analyze the Oxa1-ribosome interaction and aim to identify and characterize mitoribosome proteins which physically interact with Oxa1. The role of these ribosomal proteins in targeting the translating ribosome to the Oxa1 site and in the coupling of translation and membrane insertion events are currently being explored.

The ADP/ATP carrier protein and their assembly the with mitochondrial OXPHOS complexes

ATP produced within the mitochondria through oxidative phosphorylation (OXPHOS) is transported out of the mitochondria via metabolite carrier proteins termed the ADP/ATP carrier (AAC) protein family located within the mitochondrial inner membrane (IM). Defects in either the OXPHOS pathway or in the AAC family have been shown to underlie a number of cardiac/muscle myopathies and neurodegenerative diseases.

The central focus of our current research is the yeast AAC protein family and their demonstrated physical interaction with components of the OXPHOS complexes, specifically the cytochrome bc₁-cytochrome oxidase (COX) supercomplex and the TIM23 protein translocases of the IM. Mutations in an AAC isoform found in human cardiac and muscle tissue, the hANT1 protein, is the underlying cause of the disease autosomal-dominant progressive external ophthalmoplegia (adPEO). The onset of adPEO is characterized by a loss of COX activity and modeling of the disease in yeast has indicated that it is the structural presence of a mutated AAC family member, rather than a compromised mitochondrial ADP/ATP exchange, which causes the COX defect and the subsequent loss of the mitochondrial membrane potential and ultimate cell death. We hypothesize that the physical relationship between the AAC protein family and the cytochrome bc₁-COX-TIM23 supercomplex that we have discovered is key to understanding the molecular pathophysiology of the adPEO disease.

Selected Recent Publications

Dienhart, M.K. and R.A. Stuart 2008. The yeast Aac2 protein exists in physical association with the cytochrome bc₁-COX supercomplex and the TIM23 machinery. Mol. Biol. Cell. 19: in press

Saddar, S. Dienhart, M.K. and Stuart, R.A. 2008. The F₁F₀-ATP synthase complex influences the assembly state of the cytochrome bc₁-cytochrome oxidase supercomplex and its association with the TIM23 machinery. J. Biol. Chem., 283:6677-6686.

Jia, L., Dienhart, M.K. and Stuart, R.A.   2007.  Oxa1 directly interacts with Atp9 and mediates its assembly into the mitochondria F₁F₀-ATP synthase complex.  Mol. Biol. Cell. 18:1897-1908.

Everard-Gigot, V., Dunn, C.D., Dolan, B.M, Brunner, S., Jensen, R.E. and Stuart, R.A. 2005.Functional analysis of subunit e of the yeast F₁F₀-ATP synthase: the importance of the N-terminal membrane anchor region. Eukaryotic Cell, 4:346-355.

Jia, L., Dienhart, M., Schramp, M., McCauley, M., Hell, K. and Stuart, R.A. 2003. Yeast Oxa1 interacts with mitochondrial ribosomes: the importance of the C-terminal region of Oxa1. EMBO J., 22: 6438-6447.

Stuart, R.A. 2002. Insertion of proteins into the inner membrane of mitochondria: the role of the Oxa1 complex. Biochem. Biophys. Acta, 1592:79-87.

Current Lab Members