The human homologue of the yeast mitochondrial AAA metalloprotease Yme1p complements a yeast yme1 disruptant

AbstractIn yeast, three AAA superfamily metalloproteases (Yme1p, Afg3p and Rca1p) are localized to the mitochondrial inner membrane where they perform roles in the assembly and turnover of the respiratory chain complexes. We have investigated the function of the proposed human orthologue of yeast Yme1p, encoded by the YME1L gene on chromosome 10p. Transfection of both HEK-293EBNA and yeast cells with a green fluorescent protein-tagged YME1L cDNA confirmed mitochondrial targeting. When expressed in a yme1 disruptant yeast strain, YME1L restored growth on glycerol at 37°C. We propose that YME1L plays a phylogenetically conserved role in mitochondrial protein metabolism and could be involved in mitochondrial pathologies

The aromatic domain 66YWYWW70 of subunit VIII of the yeast ubiquinol-cytochrome c oxidoreductase is important for both assembly and activity of the enzyme

AbstractThe aromatic character of the region 66YWYWW70 of the 11-kDa subunit VIII of ubiquinol-cytochrome c oxidoreductase (bc1 complex) of the yeast Saccharomyces cerevisiae has previously been demonstrated to be important for assembly of a functional complex [Hemrika et al. (1994) FEBS Lett. 344, 15–19]. Especially the aromatic nature of residue 66 appeared to be relevant, as the very low level (5%) of bc1 complex in the mutant 66SASAA70 was restored to nearly 70% of the wild-type level in a phenotypic revertant with the sequence 66FASAA70. In the present study, three other site-directed mutants (66SAYAA70, 66SASAW70 and 66SWYWW70) were constructed and analysed. The data indicate that the presence of one aromatic residue is enough for a substantial level of assembly and that its position modulates the level of both assembly and electron transfer activity. The results also confirm the relevance of this region of subunit VIII for the formation of the Qout reaction domain, as reported by Hemrika et al. [(1993) Eur. J. Biochem. 215, 601–609]. It is further shown that the lowered specific activity of the mutant described by these authors is not due to the introduction of a cysteine in the sequence of subunit VIII

MBA1 encodes a mitochondrial membrane-associated protein required for biogenesis of the respiratory chain

AbstractThe yeast MBA1 gene (Multi-copy Bypass of AFG3) is one of three genes whose overexpression suppresses afg3-null and rcal-null mutations. Bypass of AFG3 and RCA1, whose products are essential for assembly of mitochondrial inner membrane enzyme complexes, suggests a related role for MBA1. The predicted translation product is a 30 kDa hydrophilic protein with a putative mitochondrial targeting sequence and no homology to any sequence in protein or EST databases. Gene disruption leads to a partial respiratory growth defect, which is more pronounced at temperatures above 30°C. Concomitantly, amounts of cytochromes b and aa3 are reduced. A C-terminal c-myc-tagged MBA1 gene product is functional and is found associated with the mitochondrial inner membrane, from which it can be extracted by carbonate, but not by high salt. These observations give further support to a role of MBA1 in assembly of the respiratory chain