Table of contents

Volume 2, Issue 4, pp. 94 - 138, April 2015

Issue cover
Cover: The cover is a cartoon representation of the structure of the yeast c10 ring (20 transmembrane helices (TMH), pdb, 3U2F) along with hypothetical positions of the 5 TMH of subunit a and 2 TMH of subunit b. Image by Ting Xu and David Mueller (Rosalind Franklin University of Medicine and Science, USA); modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license. Enlarge issue cover

Reviews

Translate to divide: сontrol of the cell cycle by protein synthesis

Michael Polymenis, Rodolfo Aramayo

page 94-104 | 10.15698/mic2015.04.198 | Full text | PDF | Abstract

Protein synthesis underpins much of cell growth and, consequently, cell multiplication. Understanding how proliferating cells commit and progress into the cell cycle requires knowing not only which proteins need to be synthesized, but also what determines their rate of synthesis during cell division.

Understanding structure, function, and mutations in the mitochondrial ATP synthase

Ting Xu, Vijayakanth Pagadala, David M. Mueller

page 105-125 | 10.15698/mic2015.04.197 | Full text | PDF | Abstract

The mitochondrial ATP synthase is a multimeric enzyme complex with an overall molecular weight of about 600,000 Da. The ATP synthase is a molecular motor composed of two separable parts: F1 and Fo. The F1 portion contains the catalytic sites for ATP synthesis and protrudes into the mitochondrial matrix. Fo forms a proton turbine that is embedded in the inner membrane and connected to the rotor of F1. The flux of protons flowing down a potential gradient powers the rotation of the rotor driving the synthesis of ATP. Thus, the flow of protons though Fo is coupled to the synthesis of ATP. This review will discuss the structure/function relationship in the ATP synthase as determined by biochemical, crystallographic, and genetic studies. An emphasis will be placed on linking the structure/function relationship with understanding how disease causing mutations or putative single nucleotide polymorphisms (SNPs) in genes encoding the subunits of the ATP synthase, will affect the function of the enzyme and the health of the individual. The review will start by summarizing the current understanding of the subunit composition of the enzyme and the role of the subunits followed by a discussion on known mutations and their effect on the activity of the ATP synthase. The review will conclude with a summary of mutations in genes encoding subunits of the ATP synthase that are known to be responsible for human disease, and a brief discussion on SNPs.

Research Articles

Modeling human Coenzyme A synthase mutation in yeast reveals altered mitochondrial function, lipid content and iron metabolism

Camilla Ceccatelli Berti, Cristina Dallabona, Mirca Lazzaretti, Sabrina Dusi, Elena Tosi, Valeria Tiranti, Paola Goffrini

page 126-135 | 10.15698/mic2015.04.196 | Full text | PDF | Abstract

Mutations in nuclear genes associated with defective coenzyme A biosynthesis have been identified as responsible for some forms of neurodegeneration with brain iron accumulation (NBIA), namely PKAN and CoPAN. PKAN are defined by mutations in PANK2, encoding the pantothenate kinase 2 enzyme, that account for about 50% of cases of NBIA, whereas mutations in CoA synthase COASY have been recently reported as the second inborn error of CoA synthesis leading to CoPAN. As reported previously, yeast cells expressing the pathogenic mutation exhibited a temperature-sensitive growth defect in the absence of pantothenate and a reduced CoA content. Additional characterization revealed decreased oxygen consumption, reduced activities of mitochondrial respiratory complexes, higher iron content, increased sensitivity to oxidative stress and reduced amount of lipid droplets, thus partially recapitulating the phenotypes found in patients and establishing yeast as a potential model to clarify the pathogenesis underlying PKAN and CoPAN diseases.

Microreviews

Modeling non-hereditary mechanisms of Alzheimer disease during apoptosis in yeast

Ralf J. Braun, Cornelia Sommer, Christine Leibiger, Romina J.G. Gentier, Verónica I. Dumit, Katrin Paduch, Tobias Eisenberg, Lukas Habernig, Gert Trausinger, Christoph Magnes, Thomas Pieber, Frank Sinner, Jörn Dengjel, Fred W. van Leeuwen, Guido Kroemer, Frank Madeo

page 136-138 | 10.15698/mic2015.04.199 | Full text | PDF | Abstract

Impaired protein degradation and mitochondrial dysfunction are believed to contribute to neurodegenerative disorders, including Alzheimer disease (AD). In patients suffering from non-hereditary AD, UBB+1, the frameshift variant of ubiquitin B, accumulated in neurons affected by neurofibrillary tangles, which is a pathological hallmark. We established a yeast model expressing high levels of UBB+1, and could demonstrate that UBB+1 interfered with both the ubiquitin-proteasome system (UPS) and mitochondrial function. More precisely, UBB+1 promoted the mitochondrion-localized production of the basic amino acids arginine, ornithine, and lysine, which we identified as the decisive toxic event culminating in apoptosis. Inducing the UPS activity at mitochondria prevented the lethal basic amino acid accumulation and avoided UBB+1-triggered cell loss. The arginine/ornithine metabolism is altered in brains of AD patients, and VMS1, the mitochondrion-specific UPS component, co-existed with UBB+1 in neurofibrillary tangles. Therefore, our data suggest that aberrant basic amino acid synthesis is a crucial link between UPS dysfunction and mitochondrial damage during AD progression.