The Role of mAAA protease transmembrane domain in dislocating mitochondrial inner membrane proteins

Abstract

In eukaryotic cells, the majority of mitochondrial proteins are nuclearly encoded and synthesized in the cytosol. Mitochondrial proteins are targeted to mitochondria via their targeting signals which guide them to specific compartments; outer membrane (OM), intermembrane space (IMS), inner membrane(IM), or matrix. AAA-ATPases(ATP Associated with diverse cellular Activities) are known to be involved in membrane protein degradation and biogenesis. Mitochondria carry two AAA proteases, enzymatic sites of which are in opposite side of the IM; iAAA protease in the IMS and mAAA protease in the matrix. These two AAA proteases are integral membrane proteins themselves in the IM. It has been reported that the transmembrane(TM) domains of mAAA protease is required for integral membrane protein degradation, suggesting that membrane dislocation is essential for degradation as the catalytic domain of mAAA protease is exposed to the matrix side. However, how the mAAA protease recognizes and dislocates integral membrane protein remains unknown. Besides, it is also reported that the activity of mAAA protease is accelerated in cells lacking Prohibitin, a highly conserved protein complex in eukaryotes. This study aims to elucidate the role of TM domains of mAAA protease on the membrane protein recognition and dislocation. By replacing the TM domains of Yta10 and Yta12, which are homologous subunits of mAAA protease with foreign TM segments, it is observed that when the 2nd TM of mAAA protease subunits are replaced, substrate dislocation is reduced. This suggests that the 2nd TM of mAAA proteases is critical in membrane protein dislocation. We also observed that when Prohibitin is absent, substrate dislocation is increased, implying the involvement of Prohibitin complex in dislocation activity of mAAA, and further investigation is underway.