Mutational studies of the cytochrome bc(1) complex of Rhodobacter sphaeroides

The cytochrome $bc\sb1$ complex is a multisubunit integral membrane protein. This enzyme is a central component in electron transport where it oxidizes quinol while forming a transmembrane proton gradient. The cytochrome b subunit is the locus of two distinct quinol binding sites as well as the heme groups. Despite the its importance, little is known about the $bc\sb1$ complex structure.The focus of this thesis is to identify the residues that comprise the quinol reductase (Q$\sb{\rm i}$) site in the photosynthetic bacteria Rhodobacter sphaeroides. These residues were identified by using site-directed mutagenesis and spectroscopic analysis. Since no crystal structure exists for the $bc\sb1$ complex, proposed mutations were based on sequence and inhibitor resistance data from other species. Initial results proved that the Q$\sb{\rm i}$ site function could be perturbed by the mutants and that the change in electron flow can be monitored spectroscopically. Totally conserved residues along the cytoplasmic interface were found to be essential for Q$\sb{\rm i}$ site structure. The only residues found in the cytoplasm that help define the Q$\sb{\rm i}$ site are those that can form hydrogen bonds. From this information, a helical wheel model as well as a topological map of the cytochrome b subunit were created to visualize the putative Q$\sb{\rm i}$ site domain. This represents the first experimentally-based model of the Q$\sb{\rm i}$ site.U of I OnlyETDs are only available to UIUC Users without author permissio