Lectin-Type Ubiquitin Ligase Subunits: Fbs Proteins and Their Applications for Use

Three lectin-type F-box proteins called Fbs (F-box protein-recognizing sugar chains) are found in mammals, and function as substrate-binding subunits in the SCF (Skp1/Cullin1/F-box protein) complex ubiquitin ligases. The SCF^Fbs recognizes cytosolic N-glycans as a signal for an adverse cellular state, and ubiquitinates glycoproteins which appear in the cytosol to remove them from cells. Although Fbs proteins recognize innermost Man₃GlcNAc₂ structure that is commonly found in most N-glycan structures, they preferentially bind high-mannose-type glycans. Recently, the recombinant Fbs1 derivative protein has been developed as a tool for comprehensive enrichment of N-glycopeptides. The labeled Fbs3 is also available as a tool for detecting organelle damage in cells as it has characteristic properties which cause it to quickly accumulate in damaged organelles. In this chapter, we introduce two applications of use for Fbs proteins: the unbiased N-glycopeptide capture method and the detection of damaged organelles in living cells.