bims-cytox1 2021-03-28 papers

Issue of 2021–03–28
two papers selected by
Gavin McStay, Staffordshire University

Eur J Med Genet. 2021 Mar 18. pii: S1769-7212(21)00061-6. [Epub ahead of print] 104195

A novel variant in the COX15 gene causing a fatal infantile cardioencephalomyopathy: a case report with clinical and molecular review.

Manuella Galvão de Oliveira, Célia Tengan, Cecília Micheletti, Paloma Ramos de Macedo, Mirlene Cecília Soares Pinho Cernach, Thiago Rodrigues Cavole, Marina de França Basto, Joselito Sobreira Filho, Luiza Amaral Virmond, Fernanda Milanezi, Viviane Nakano, Ariane Falconi, Eduardo Perrone.

The cytochrome c-oxidase (COX) enzyme, also known as mitochondrial complex IV (MT-C4D), is a transmembrane protein complex found in mitochondria. COX deficiency is one of the most frequent causes of electron transport chain defects in humans. Therefore, high energy demand organs and tissues are affected in patients with mutations in the COX15 gene, with variable phenotypic expressiveness. We describe the case of a male newborn with hypertrophic cardiomyopathy and serum and cerebrospinal fluid hyperlacticaemia, whose exome sequencing revealed two variants in a compound heterozygous state: c.232G>A;p.(Gly78Arg), classified as likely pathogenic, and c.452C>G;p.(Ser151Ter), as pathogenic; the former never previously described in the literature.

Keywords: COX15; Cytochrome c oxidase; complex IV; hyperlacticaemia; hypertrophic cardiomyopathy

DOI: https://doi.org/10.1016/j.ejmg.2021.104195

Proc Natl Acad Sci U S A. 2021 Mar 30. pii: e2100558118. [Epub ahead of print]118(13):

TMEM70 and TMEM242 help to assemble the rotor ring of human ATP synthase and interact with assembly factors for complex I.

Joe Carroll, Jiuya He, Shujing Ding, Ian M Fearnley, John E Walker.

Human mitochondrial ATP synthase is a molecular machine with a rotary action bound in the inner organellar membranes. Turning of the rotor, driven by a proton motive force, provides energy to make ATP from ADP and phosphate. Among the 29 component proteins of 18 kinds, ATP6 and ATP8 are mitochondrial gene products, and the rest are nuclear gene products that are imported into the organelle. The ATP synthase is assembled from them via intermediate modules representing the main structural elements of the enzyme. One such module is the c8-ring, which provides the membrane sector of the enzyme's rotor, and its assembly is influenced by another transmembrane (TMEM) protein, TMEM70. We have shown that subunit c interacts with TMEM70 and another hitherto unidentified mitochondrial transmembrane protein, TMEM242. Deletion of TMEM242, similar to deletion of TMEM70, affects but does not completely eliminate the assembly of ATP synthase, and to a lesser degree the assembly of respiratory enzyme complexes I, III, and IV. Deletion of TMEM70 and TMEM242 together prevents assembly of ATP synthase and the impact on complex I is enhanced. Removal of TMEM242, but not of TMEM70, also affects the introduction of subunits ATP6, ATP8, j, and k into the enzyme. TMEM70 and TMEM242 interact with the mitochondrial complex I assembly (the MCIA) complex that supports assembly of the membrane arm of complex I. The interactions of TMEM70 and TMEM242 with MCIA could be part of either the assembly of ATP synthase and complex I or the regulation of their levels.

Keywords: ATP synthase; TMEM242; TMEM70; assembly; human mitochondria

DOI: https://doi.org/10.1073/pnas.2100558118