Regulation of mitochondrial phospholipids by Ups1/PRELI-like proteins depends on proteolysis and Mdm35

The mitochondrial phospholipid metabolism critically depends on members of the conserved Ups1/PRELI-like protein family in the intermembrane space. Ups1 and Ups2 (also termed Gep1) were shown to regulate the accumulation of cardiolipin (CL) and phosphatidylethanolamine (PE), respectively, in a lipid-specific but coordinated manner. It remained enigmatic, however, how the relative abundance of both phospholipids in mitochondrial membranes is adjusted on the molecular level. Here, we describe a novel regulatory circuit determining the accumulation of Ups1 and Ups2 in the intermembrane space. Ups1 and Ups2 are intrinsically unstable proteins, which are degraded by distinct mitochondrial peptidases. The turnover of Ups2 is mediated by the i-AAA protease Yme1, whereas Ups1 is degraded by both Yme1 and the metallopeptidase Atp23. We identified Mdm35, a member of the twin Cx(9)C protein family, as a novel interaction partner of Ups1 and Ups2. Binding to Mdm35 ensures import and protects both proteins against proteolysis. Homologues to all components of this pathway are present in higher eukaryotes, suggesting that the regulation of mitochondrial CL and PE levels is conserved in evolution.

Regulation of mitochondrial phospholipids by Ups1/PRELI-like proteins depends on proteolysis and Mdm35

The mitochondrial phospholipid metabolism critically depends on members of the conserved Ups1/PRELI-like protein family in the intermembrane space. Ups1 and Ups2 (also termed Gep1) were shown to regulate the accumulation of cardiolipin (CL) and phosphatidylethanolamine (PE), respectively, in a lipid-specific but coordinated manner. It remained enigmatic, however, how the relative abundance of both phospholipids in mitochondrial membranes is adjusted on the molecular level. Here, we describe a novel regulatory circuit determining the accumulation of Ups1 and Ups2 in the intermembrane space. Ups1 and Ups2 are intrinsically unstable proteins, which are degraded by distinct mitochondrial peptidases. The turnover of Ups2 is mediated by the i-AAA protease Yme1, whereas Ups1 is degraded by both Yme1 and the metallopeptidase Atp23. We identified Mdm35, a member of the twin Cx(9)C protein family, as a novel interaction partner of Ups1 and Ups2. Binding to Mdm35 ensures import and protects both proteins against proteolysis. Homologues to all components of this pathway are present in higher eukaryotes, suggesting that the regulation of mitochondrial CL and PE levels is conserved in evolution.

Prohibitins interact genetically with Atp23, a novel processing peptidase and chaperone for the F1Fo-ATP synthase

The generation of cellular energy depends on the coordinated assembly of nuclear and mitochondrial-encoded proteins into multisubunit respiratory chain complexes in the inner membrane of mitochondria. Here, we describe the identification of a conserved metallopeptidase present in the intermembrane space, termed Atp23, which exerts dual activities during the biogenesis of the F(1)F(O)-ATP synthase. On one hand, Atp23 serves as a processing peptidase and mediates the maturation of the mitochondrial-encoded F(O)-subunit Atp6 after its insertion into the inner membrane. On the other hand and independent of its proteolytic activity, Atp23 promotes the association of mature Atp6 with Atp9 oligomers. This assembly step is thus under the control of two substrate-specific chaperones, Atp10 and Atp23, which act on opposite sides of the inner membrane. Strikingly, both ATP10 and ATP23 were found to genetically interact with prohibitins, which build up large, ring-like assemblies with a proposed scaffolding function in the inner membrane. Our results therefore characterize not only a novel processing peptidase with chaperone activity in the mitochondrial intermembrane space but also link the function of prohibitins to the F(1)F(O)-ATP synthase complex.

[Precision of lenticular thickness in relation to full stroma corneal thickness. Experimental results with the lamellar microkeratome]

In this study 150 pig corneas and 20 human corneas were dissected with an automatic rotating microkeratome for lamellar grafting. The cornea thickness varied between 0.507 mm and 0.829 with an average 0.66 mm. The aim of this investigation was to show the influence of corneal thickness, the chosen diameter and spacing on the precision of cutting lenticles. We did ten series: the pig corneas were dissected at three different intervals of 0.15, 0.25, 0.35 mm and diameters of 9 and 6mm. The human corneas were cut at intervals of 0.4 mm and 0.25 mm and with diameter of 9 and 7 mm. Although the pig corneas were fresh, the intraocular pressure was too low. It was raised with an injection of physiological salt solution to a predefined level. The rotating speed of the trephine blade, the speed of blade advancement and lubrication fluid were kept constant. Ultrasound pachymetry was performed on the center of the corneas before cutting had on the lenticles afterward. We showed that a thick corneal diameter had a negative influence, i.e., the greater the diameter, the lesser the precision; the same was true for the corneal thickness. On the other hand, the intervals had just the opposite effect: the closer they were, the better the correlation. The human eye results were different in quantity but not in tendency, with less striking effects. The average variation for pig corneas was 22% and for human eyes 8%. The best results were received with a large interval, a small diameter, and a normal corneal thickness in human eyes.