| dc.description.abstracteng | The respiratory chain in the inner membrane of the yeast mitochondrion is organized as a network of individual complexes and large supercomplex structures. These supercomplexes are composed of dimeric complex III and one or two copies of complex IV (III2IV and III2IV2). Even though the existence of respiratory supercomplexes has been shown for a variety of organisms, it is not fully understood which purpose they serve and how they are assembled as well as regulated. Lipids, protein complexes and single proteins were proposed to take part in these intricate processes. To the latter group of potential supercomplex regulators belongs the Rcf protein family which is composed of three related proteins: Rcf1, Rcf2 and the so far uncharacterized YBR255C-A/ Rcf3. Rcf1 was shown to be essential for the formation of III2IV2. To obtain a deeper understanding of the role of the Rcf protein family in supercomplex formation and stability, this study aimed at an in depth investigation of Rcf2 and Rcf3.
Like Rcf1 and Rcf2, Rcf3 proved to be a constituent of supercomplexes via its association with complex IV*, an Rcf-specific version of complex IV. All three Rcfs furthermore revealed the ability to interact with complex III in the absence of complex IV, positioning them at the interface of both complexes. In contrast to Rcf1, Rcf3 and Rcf2 are dispensable for supercomplex formation. However, despite unchanged supercomplex organization, simultaneous deletion of RCF2 and RCF3 leads to severely reduced respiratory growth. This indicates a functional overlap, which is further supported by the sequence similarities of Rcf3 with the N-terminus of Rcf2 and the observed processing of Rcf2. This study revealed that Rcf2 is subjected to limited proteolysis after import into mitochondria. The resulting N terminal fragment, Rcf2N, was neither observed in individual complexes nor in supercomplexes. Whether it is degraded or preserved to fulfill a regulatory function within the respiratory chain could not be clarified on the basis of the present data. In contrast, the C terminal fragment, Rcf2C, is assembled into complex IV* along with the remaining full length Rcf2. It was hence found in supercomplexes. Further investigations will elucidate its function and the significance of the processing event in regard to supercomplex organization. | de |