Alternative topogenesis of Mgm1 and mitochondrial morphology depend on ATP and a functional import motor

Abstract

Mitochondrial morphology and inheritance of mitochondrial DNA in yeast depend on the dynamin-like GTPase Mgm1. It is present in two isoforms in the intermembrane space of mitochondria both of which are required for Mgm1 function. Limited proteolysis of the large isoform by the mitochondrial rhomboid protease Pcp1/Rbd1 generates the short isoform of Mgm1 but how this is regulated is unclear. We show that near its NH2 terminus Mgm1 contains two conserved hydrophobic segments of which the more COOH-terminal one is cleaved by Pcp1. Changing the hydrophobicity of the NH2-terminal segment modulated the ratio of the isoforms and led to fragmentation of mitochondria. Formation of the short isoform of Mgm1 and mitochondrial morphology further depend on a functional protein import motor and on the ATP level in the matrix. Our data show that a novel pathway, to which we refer as alternative topogenesis, represents a key regulatory mechanism ensuring the balanced formation of both Mgm1 isoforms. Through this process the mitochondrial ATP level might control mitochondrial morphology.

Quality Control of Mitochondrial Proteostasis

“…The IM rhomboid protease, Pcp1, is responsible for cleavage of Mgm1 in yeast (McQuibban et al 2003;Sesaki et al 2003;Herlan et al 2004). The mammalian homolog of Pcp1, PARL, has been linked to the release of short OPA1 isoforms from mitochondria during apoptosis and suggested to play a role in OPA1 processing (Cipolat et al 2006).…”

Dislocation by the m-AAA Protease Increases the Threshold Hydrophobicity for Retention of Transmembrane Helices in the Inner Membrane of Yeast Mitochondria

“…In the alternative topogenesis model for import of Mgm1 (11), the first hydrophobic segment integrates into the membrane in 30 -40% of the molecules (arrow d), resulting in membrane-anchored l-Mgm1. For the remaining molecules, the first hydrophobic segment translocates into the matrix (arrow e), and the second hydrophobic segment is processed by Pcp1 (arrow f), generating s-Mgm1 in the intermembrane space (11). B, the model proteins Ccp1, Mgm1, and CoxVaT-Mgm1.…”

“…During its passage through the TIM23 translocon, the hydrophobic segment is inserted laterally into the inner membrane, yielding the long form of Mgm1 (l-Mgm1), but only in ϳ30 -40% of the molecules. In the remaining molecules, the hydrophobic segment is translocated into the matrix, and the protein is then cleaved by Pcp1 in a downstream, second hydrophobic segment, giving rise to a shorter form of the protein (s-Mgm1) (10,11). Translocation of the first hydrophobic segment across the inner membrane is mediated by the matrix-localized mitochondrial import motor (3,11).…”

Quality control of mitochondria during aging: Is there a good and a bad side of mitochondrial dynamics?

“…In this context it is important to note that it was shown in yeast as well as in mammalian cells that the bioenergetic state of mitochondria is linked to the mitochondrial morphology [41,42,45,46]. When mitochondrial function is impaired, the fusion machinery is inactivated, e.g.…”

“…Damaged mitochondria are subsequently marked by stabilization of PINK1 at the outer membrane and by recruitment of PARKIN [17,18] which represent early steps in mitophagy. Based on these observations the life cycle of single mitochondria within the network was inferred and it was proposed that it ensures quality control and maintenance of the mitochondrial network as a whole [15,46,[51][52][53].…”