Cooperative function of Fmp30, Mdm31, and Mdm32 in Ups1-independent cardiolipin accumulation in the yeast Saccharomyces cerevisiae

Abstract

Cardiolipin (CL) is synthesized from phosphatidic acid (PA) through a series of enzymatic reactions occurring at the mitochondrial inner membrane (MIM). Ups1-Mdm35 mediates PA transfer from the mitochondrial outer membrane (MOM) to the MIM in the yeast Saccharomyces cerevisiae. Deletion of UPS1 leads to a ~80% decrease in the cellular CL level. However, the CL accumulation in ups1∆ cells is enhanced by the depletion of Ups2, which forms a protein complex with Mdm35 and mediates phosphatidylserine (PS) transfer from the MOM to the MIM for phosphatidylethanolamine (PE) synthesis by a PS decarboxylase, Psd1. In this study, we found that the accumulation of CL in ups1∆ cells was enhanced by deletion of not only UPS2, but also PSD1 and CHO1 encoding a PS synthase, suggesting that low PE levels in mitochondria were relevant to the enhancement of CL accumulation in ups1∆ cells. Furthermore, the Ups1-independent and low-level PE-enhanced CL accumulation was shown to depend on the functions of FMP30, MDM31, and MDM32. In addition, the physical interactions of Fmp30 with Mdm31 and Mdm32 were revealed. Thus, when the mitochondrial PE level is reduced, Fmp30, Mdm31, and Mdm32 seem to function cooperatively for the accumulation of CL in a UPS1-independent manner.

Porin proteins have critical functions in mitochondrial phospholipid metabolism in yeast

“…Deletion of UPS1 reduced the CL level to ϳ20% of that in WT cells, and the CL level was largely restored on concomitant deletion of UPS2 in ups1⌬ cells (Fig. 3, A and B, lanes 1-3), thus being consistent with previous reports (17,18,26). Depletion of porin proteins in the ups1⌬ ups2⌬ background as well as the UPS1 UPS2 background greatly reduced the CL level ( Fig.…”

“…In the present study, we identified a yeast porin protein, Por1 as a protein interacting with the MIM protein Mdm31 (Fig. 1) that is required for Ups1-independent and low mitochondrial PE-enhanced accumulation of CL (26). In addition, we found that Por1 also interacts with the IMS protein Mdm35 (Fig.…”

“…The substrates of Fmp30 remain to be established, but analyses of Fmp30 with point mutations have revealed that the hydrolase activity of Fmp30 is required for its function (33). It is also noteworthy that physical interactions of Fmp30 with Mdm31 and Mdm32 were revealed previously (26). Moreover, interaction of porin proteins and Mdm31 might trigger the Mdm31, Mdm32, or Fmp30 function.…”

“…However, as shown in Fig. 1, Por1 was found to interact with Mdm31, which, as well as Mdm32 and Fmp30, is required for the Ups1independent CL accumulation that is enhanced under low mitochondrial PE conditions such as those in ups2⌬, psd1⌬, and cho1⌬ cells (26). Therefore, we examined the effect of depletion of porin proteins on the Ups1-independent CL accu-mulation, namely, the CL level in ups1⌬ ups2⌬ cells.…”

Phosphatidylethanolamine made in the inner mitochondrial membrane is essential for yeast cytochromebc1complex function

“…Our results strongly indicate that when Psd1p is missing or mis-localized, a minimal threshold of PE is not achieved within the IM that is necessary to accumulate normal levels of CL and promote the full activity of the OXPHOS machinery. Although it is presently unclear how the Kennedy Pathway for PE production promotes CL accumulation, it is known that the Ups1p and Ups2p lipid trafficking proteins have an inverse relationship with respect to CL/PE metabolism suggesting that this may be linked to PS/PA trafficking into the IM 3, 54, 55 . Depletion of PS in the psd1 Δ psd2 Δ background restored CL levels to that of psd1 Δ and cho1 Δ which were still comparatively reduced vs WT (Fig 7G).…”