title: Spectrin and ubiquitination: a review.
abstract: This review covers the observations leading to the conclusion that erythrocyte spectrin is a chimeric E2/E3 ubiquitin conjugating/ligating enzyme and the impact of this activity on the cell. Spectrin is important for the shape and the physical properties of the red blood cell, such as deformability and resistance to mechanical stress. The involvement of RBC spectrin in the ubiquitination process has been demonstrated. Human erythrocyte alpha-spectrin can facilitate formation of ubiquitin-spectrin adducts and conjugates in cell free systems (28). Computer analysis revealed domains that contained significant homologies to known consensus catalytic E2 and E3 sequences, and allowed us to develop a model for alpha-spectrin ubiquitin conjugating enzyme (E2) and ubiquitin protein ligase (E3) enzymatic activities. The model has been tested and the precise E2/E3 site(s) identified by site-specific mutational analyses using a GST-fusion alpha-spectrin(2005-2415) recombinant in an in vitroubiquitination assay (26). The results indicated that cysteine 2071 and cysteine 2100 are critical for alpha-spectrin(2005-2415) E2/E3 activity as expected. However, both Cys2071 and Cys2100 are capable of transferring ubiquitin from an E1 enzyme to target sites within alpha-spectrin(2005-2415). This revealed a redundancy of function for human RBC spectrin's chimeric E2/E3 ubiquitin conjugating/ligating activity. Since spectrin is the major structural component of the erythrocyte membrane skeleton, and it constitutes 20% of the total RBC membrane protein, its ubiquitination enzymatic activity could play an important role in both erythropoietic cells and mature RBCs. This could also be one reason for evolving this redundancy of function.
authors.affiliation: Institute of Biomedical Sciences and Technology, Sickle Cell Disease Research Center, Dept. of Molecular and Cell Biology, University of Texas at Dallas, Richardson, TX 75083, USA.
authors.forename: Y-J
authors.initials: YJ
authors.lastname: Hsu
authors.forename: S R
authors.initials: SR
authors.lastname: Goodman
mesh_terms: D006801:Humans; D008958:Models, Molecular; D013049:Spectrin / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000737:chemistry / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism
chemical_list: D025801:Ubiquitin; D013049:Spectrin; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases