The SKP1/Cullin/F-box (SCF) class of E3 Ubiquitin Ligases is an evolutionarily conserved family of enzymes that regulate key cellular processes including the cell cycle, membrane trafficking, and signaling. The SCF-E3 is composed of four core components - Rbx1, Cullin1, SKP1, and a F-box protein. F-box proteins are the subunits that recruit substrate proteins to be poly-ubiquitinated by the SCF-E3, and they can also be directly poly-ubiquitinated. SCF-E3 dependent polyubiquitin serves as a signal for targeting to and degradation by the 26S-proteasome. Every eukaryote expresses a repertoire of F-box proteins, the majority of which have different affinities for different substrate proteins. Thus, F-box proteins are critical since they dictate which specific proteins will be ubiquitinated by the SCF-E3. In addition, F-box proteins can function independently of the SCF-E3. Thus, identifying and characterizing F-box proteins is central to understanding the functions of the SCF-E3 and remodeling of the proteome as cells engage new functions. This is important because protein degradation is as important as gene transcription in defining a cell's proteome. Here, we will identify essential SCF-E3 dependent F-box proteins, determine why they are essential, and identify the proteins that are their ubiquitination substrates. These studies will reveal how ubiquitin supports growth and virulence of a major human parasite. In addition, these findings will be relevant to related pathogens given the conservation of the SCF- E3 and many F-box proteins between Toxoplasma and other apicomplexan parasites.
Regulated protein degradation is an important way that cells regulate their functions. But how this occurs in human parasites is largely unknown. This work seeks to identify the factors that determine which proteins will be degraded as a parasite grows.