Sesaki Hiromi, Southard Sheryl M, Hobbs Alyson E Aiken, Jensen Robert E
Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Biochem Biophys Res Commun. 2003 Aug 22;308(2):276-83. doi: 10.1016/s0006-291x(03)01348-2.
The dynamin-related GTPase, Mgm1p, is critical for the fusion of the mitochondrial outer membrane, maintenance of mitochondrial DNA (mtDNA), formation of normal inner membrane structures, and inheritance of mitochondria. Although there are two forms of Mgm1p, 100 and 90 kDa, their respective functions and the mechanism by which these two forms are produced are not clear. We previously isolated ugo2 mutants in a genetic screen to identify components involved in mitochondrial fusion [J. Cell Biol. 152 (2001) 1123]. In this paper, we show that ugo2 mutants are defective in PCP1, a gene encoding a rhomboid-related serine protease. Cells lacking Pcp1p are defective in the processing of Mgm1p and produce only the larger (100 kDa) form of Mgm1p. Similar to mgm1delta cells, pcp1delta cells contain partially fragmented mitochondria, instead of the long tubular branched mitochondria of wild-type cells. In addition, pcp1delta cells, like mgm1delta cells, lack mtDNA and therefore are unable to grow on nonfermentable medium. Mutations in the catalytic domain lead to complete loss of Pcp1p function. Similar to mgm1delta cells, the fragmentation of mitochondria and loss of mtDNA of pcp1delta cells were rescued when mitochondrial division was blocked by inactivating Dnm1p, a dynamin-related GTPase. Surprisingly, in contrast to mgm1delta cells, which are completely defective in mitochondrial fusion, pcp1delta cells can fuse their mitochondria after yeast cell mating. Our study demonstrates that Pcp1p is required for the processing of Mgm1p and controls normal mitochondrial shape and mtDNA maintenance by producing the 90 kDa form of Mgm1p. However, the processing of Mgm1p is not strictly required for mitochondrial fusion, indicating that the 100 kDa form is sufficient to promote fusion.
与发动蛋白相关的GTP酶Mgm1p对于线粒体外膜融合、线粒体DNA（mtDNA）的维持、正常内膜结构的形成以及线粒体遗传至关重要。尽管存在两种形式的Mgm1p，即100 kDa和90 kDa，但它们各自的功能以及这两种形式产生的机制尚不清楚。我们之前在一项遗传筛选中分离出ugo2突变体，以鉴定参与线粒体融合的成分[《细胞生物学杂志》152(2001)1123]。在本文中，我们表明ugo2突变体在PCP1中存在缺陷，PCP1是一个编码类菱形丝氨酸蛋白酶的基因。缺乏Pcp1p的细胞在Mgm1p的加工过程中存在缺陷，并且只产生较大（100 kDa）形式的Mgm1p。与mgm1δ细胞类似，pcp1δ细胞含有部分碎片化的线粒体，而不是野生型细胞中长管状分支的线粒体。此外，pcp1δ细胞与mgm1δ细胞一样，缺乏mtDNA，因此无法在非发酵培养基上生长。催化结构域中的突变导致Pcp1p功能完全丧失。与mgm1δ细胞类似，当通过使与发动蛋白相关的GTP酶Dnm1p失活来阻断线粒体分裂时，pcp1δ细胞线粒体的碎片化和mtDNA的丢失得以挽救。令人惊讶的是，与线粒体融合完全缺陷的mgm1δ细胞不同，pcp1δ细胞在酵母细胞交配后能够融合它们的线粒体。我们的研究表明，Pcp1p是Mgm1p加工所必需的，并且通过产生90 kDa形式的Mgm1p来控制正常的线粒体形态和mtDNA维持。然而，Mgm1p的加工对于线粒体融合并非严格必需的，这表明100 kDa形式足以促进融合。
