Structural features in the signal sequence required for its removal by the mitochondrial processing peptidase
Abstract
Most mitochondrial proteins are encoded in the nucleus and translated in the cytoplasm with an N-terminal extension called the signal sequence, which directs these proteins to the various mitochondrial subcompartments. Subsequent to reaching the matrix space, the signal sequence is removed by the mitochondrial processing peptidase (MPP). Additionally, a small group of proteins, such as the matrix enzyme, rhodanese, possess a signal sequence which is not removed. Little is known about regions of the signal peptide which allow for processing to occur. The purpose of this thesis is to explore structural features in the signal sequence which are essential for its removal by MPP. By making rhodanese processable, it was demonstrated that both a cleavage site and structural elements prior to this site are necessary for removal of the signal sequence. It was further shown that the secondary structure at the N-terminal of a signal sequence did not influence processing. However, the number of arginine residues in this region affected processing efficiency. Additionally, studies with the signal sequence from aldehyde dehydrogenase revealed that MPP may not remove a signal sequence if the processing site is part of a stable helix. MPP is soluble in the mitochondrial matrix in rat liver and is membrane-bound in spinach. The processing activity from mammals and plants was compared and it was revealed that the enzyme from both species recognized similar structural features in the signal sequence, even though these enzymes have different localizations. Additional work focused on mitochondrial import and the influence of the mature protein on this process. It was shown that the mature protein may destabilize the signal sequence and that the signal sequence and mature protein must be compatible for import to occur. It can be concluded that different regions of a signal sequence are necessary for import and for processing by MPP.
Degree
Ph.D.
Advisors
Weiner, Purdue University.
Subject Area
Biochemistry|Molecular biology
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