Identification of the mitochondrial receptor complex in Saccharomyces cerevisiae

Abstract

Mitochondrial protein import involves the recognition of preproteins by receptors and their subsequent translocation across the outer membrane. In Neurospora crassa, the two import receptors, MOM19 and MOM72, were found in a complex with the general insertion protein, GIP (formed by MOM7, MOM8, MOM30 and MOM38) and MOM22. We isolated a complex out of S. cerevisiae mitochondria consisting of MOM38/ISP42, the receptor MOM72, and five new yeast proteins, the putative equivalents of N. crassa MOM7, MOM8, MOM19, MOM22 and MOM30. A receptor complex isolated out of yeast cells transformed with N. crassa MOM19 contained the N. crassa master receptor in addition to the yeast proteins. This demonstrates that the yeast complex is functional, and provides strong evidence that we also have identified the yeast MOM19.

Mitochondrial protein import: Mechanisms, components and energetics

“…The characterisation of these mutant N. crassa cells demonstrated the important role of MOM19 in precursor import: cells in which the MOM19 gene was inactivated stopped to grow, the mitochondria lost their protein synthesis activity as well as their respiratory complexes [9]. Lysis of N. crassa mitochondria with mild detergents and subsequent immunoprecipitation with anti-MOM19 antibodies revealed that MOM19 is present in a complex with MOM72 and a number of other proteins of 7, 8, 22 and 38 kDa (MOM7, MOM8, MOM22 and MOM38) [10]. MOM38 turned out to be considerably more proteinase-resistant than the two receptors, MOM19 and MOM72.…”

“…MOM22 appears to promote the initial entrance of the receptor-bound precursors into a General Insertion Pore (GIP) which consists of MOM38 and probably MOM7, MOM8 in N. crassa, or ISP42, ISP6 and probably other components in S. cerecisiae. The GIP-complex can be co-immunoprecipitated with antibodies against MOM19 [10]. Evidence for the existence of a general insertion pore has been obtained from the observation that this site can be saturated by chemical amounts of porin precursors [16] and that the ADP/ATP carrier in the absence of a membrane potential can accumulate at the GIP-site in a proteinase-protected location [17].…”

Mitochondrial protein import: Specific recognition and membrane translocation of preproteins

“…Yeast mitochondria contain a receptor/import complex with a similar protein composition as found in N. crassa mitochondria (Moczko et al, 1992). So far, three of the components of this yeast complex have been identified.…”

“…What could be the molecular nature of these proteinaceous pores? In N. crassa and in S. cerevisiae (Moczko et al, 1992), the two import receptors MOM19 and MOM72 are found in a high molecular weight complex in the mitochondrial outer membrane. In both organisms, the complex contains at least five additional proteins of 7, 8, 22, 30 and 38 kD (Table), termed MOM7, MOM8, MOM22, MOM30 and MOM38 Moczko et al, 1992;S611ner et al, 1992).…”

“…In N. crassa and in S. cerevisiae (Moczko et al, 1992), the two import receptors MOM19 and MOM72 are found in a high molecular weight complex in the mitochondrial outer membrane. In both organisms, the complex contains at least five additional proteins of 7, 8, 22, 30 and 38 kD (Table), termed MOM7, MOM8, MOM22, MOM30 and MOM38 Moczko et al, 1992;S611ner et al, 1992). This mitochondrial receptor complex is thought to represent the translocation machinery of the outer membrane organized in a cooperating multi-subunit complex as found in other biological systems (A1-berts & Miake-Lye, 1992).…”