Mitochondrial protein import requires multiple energy sources, types of signals,
ID: 167208 • Letter: M
Question
Mitochondrial protein import requires multiple energy sources, types of signals, and pore complexes. Consider the require- ments needed for import and proper processing of four different types of mitochondrial proteins: 1) a matrix enzyme (alcohol dehydrogenase), 2) an inter-membrane space protein (cytochrome c), 3) an inner membrane transmembrane protein (cytochrome oxidase Va), and 4) an outer membrane transmembrane protein (porin). Indicate which components are required for proper location and maturation of each of these proteins Use a “+” to indicate required and “-” not required.
TIM complex Matrix chaperones nner membrane space protease cytosolic chaperones alcohol dehydrogenase cytochrome c cytochrome oxidase Va porinExplanation / Answer
Various proteinaceues signalling moleucles and enzymes move to and fro the mitochondria to perform various functions such as redox balance, apoptosis and cellular oxidative phosphorylation maintenance. Many proteins are transported inside or outside the mitochondria in response to a signalling event. The requirement of various mitochondrial components can be described as tabulated and discussed below:
1. Alcohol dehydrogenase: This enzyme is required for alcohol degradation and a fraction of it is found inside the mitochondria. This fraction moves into the mitochondria via mitochondrial trans-membrane proteins such a mortalin and TIM/TOM complexes.
2. Cytochrome c: This is a transmembrane protein residing across the membrane of the mitochondria. This protein is a death-signal molecule and is released after proteolytic cleavage of cytosolic proteins. As cytochrome c is released from mitochondria, cellular apoptosis is activated.
3. Cytochrome oxidase Va or COX: This enzymes resides inside the mitochondrial matrix and is essentially required for maintenance of mitochondrial electron transport chain complex activities along with oxidative phosphorylation via maintenance of redox balance. By activity of cellular and matrix chaperones, this enzyme is transloated outside or degraded in the mitochondria.
4. Porin: Porin represent a class of mitochondrial membrane proteins which modulate transport of materials inside and outside. They require the action of TIM/TOM complexes but not chaperonic activity for cleavage of the target.
TIM Complex Matrix Chaperones Inner membrane space protease Cytosolic chaperones Alcohol dehydrogenase + - - - cytochrome c + - + + cytochrome oxidase Va - + - + Porin + - - -