Exists either covalently attached to another protein, or free (unanchored). When covalently bound, it is conjugated to target proteins via an isopeptide bond either as a monomer (monoubiquitin), a polymer linked via different Lys residues of the ubiquitin (polyubiquitin chains) or a linear polymer linked via the initiator Met of the ubiquitin (linear polyubiquitin chains). Polyubiquitin chains, when attached to a target protein, have different functions depending on the Lys residue of the ubiquitin that is linked: Lys-6-linked may be involved in DNA repair; Lys-11-linked is involved in ERAD (endoplasmic reticulum-associated degradation) and in cell-cycle regulation; Lys-29-linked is involved in proteotoxic stress response and cell cycle; Lys-33-linked is involved in kinase modification; Lys-48-linked is involved in protein degradation via the proteasome; Lys-63-linked is involved in endocytosis, DNA-damage responses as well as in signaling processes leading to activation of the transcription factor NF-kappa-B. Linear polymer chains formed via attachment by the initiator Met lead to cell signaling. Ubiquitin is usually conjugated to Lys residues of target proteins, however, in rare cases, conjugation to Cys or Ser residues has been observed. When polyubiquitin is free (unanchored-polyubiquitin), it also has distinct roles, such as in activation of protein kinases, and in signaling.
Background References
1. Yu Y., Zheng Q., Erramilli S.K., Pan M., Park S., Xie Y., Li J., Fei J., Kossiakoff A.A., Liu L., Zhao M. K29-linked ubiquitin signaling regulates proteotoxic stress response and cell cycle. Nat. Chem. Biol. 17:896-905(2021).
2. Huang F., Kirkpatrick D., Jiang X., Gygi S.P., Sorkin A. Differential regulation of EGF receptor internalization and degradation by multiubiquitination within the kinase domain. Mol. Cell 21:737-748(2006)
Immunohistochemical analysis of paraffin-embedded human kidney tissue with Rabbit anti-RPS27A antibody (HA500371) at 1/400 dilution.
The section was pre-treated using heat mediated antigen retrieval with sodium citrate buffer (pH 6.0) (high pressure) for 2 minutes. The tissues were blocked in 1% BSA for 20 minutes at room temperature, washed with ddH2O and PBS, and then probed with the primary antibody (HA500371) at 1/400 dilution for 1 hour at room temperature. The detection was performed using an HRP conjugated compact polymer system. DAB was used as the chromogen. Tissues were counterstained with hematoxylin and mounted with DPX.
Immunocytochemistry analysis of A172 cells labeling RPS27A with Rabbit anti-RPS27A antibody (HA500371) at 1/200 dilution.
Cells were fixed in 4% paraformaldehyde for 10 minutes at 37 ℃, permeabilized with 0.05% Triton X-100 in PBS for 20 minutes, and then blocked with 2% negative goat serum for 30 minutes at room temperature. Cells were then incubated with Rabbit anti-RPS27A antibody (HA500371) at 1/200 dilution in 2% negative goat serum overnight at 4 ℃. Goat Anti-Rabbit IgG H&L (iFluor™ 488, HA1121) was used as the secondary antibody at 1/1,000 dilution. PBS instead of the primary antibody was used as the secondary antibody only control. Nuclear DNA was labelled in blue with DAPI.
Immunocytochemistry analysis of A375 cells labeling RPS27A with Rabbit anti-RPS27A antibody (HA500371) at 1/200 dilution.
Cells were fixed in 4% paraformaldehyde for 10 minutes at 37 ℃, permeabilized with 0.05% Triton X-100 in PBS for 20 minutes, and then blocked with 2% negative goat serum for 30 minutes at room temperature. Cells were then incubated with Rabbit anti-RPS27A antibody (HA500371) at 1/200 dilution in 2% negative goat serum overnight at 4 ℃. Goat Anti-Rabbit IgG H&L (iFluor™ 488, HA1121) was used as the secondary antibody at 1/1,000 dilution. PBS instead of the primary antibody was used as the secondary antibody only control. Nuclear DNA was labelled in blue with DAPI.
Western blot analysis of RPS27A on different lysates with Rabbit anti-RPS27A antibody (HA500371) at 1/5,000 dilution.
Lane 1: HeLa (Human cervical adenocarcinoma cell)cell lysate
Exposure time: 25 seconds; ECL: K1801
Blocking: 5% NFDM/TBST, 1 hour at room temperature Primary antibody: HA500371, 1/5,000 in primary antibody dilution buffer (K1803), overnight at 4 ℃ Secondary antibody: Goat anti-Rabbit IgG-HRP (HA1001), 1/50,000 in 5% NFDM/TBST, 1 hour at room temperature
Predicted band size: 18.0 kDa Observed band size: 10-15 kDa
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