Polyubiquitin-B [Cleaved into: Ubiquitin]
1_MQIFV 6_ KTLTG 11_ KTITL 16_ EVEPS 21_ DTIEN 26_ VKAKI 31_ QDKEG 36_ IPPDQ 41_ QRLIF 46_ AGKQL 51_ EDGRT 56_ LSDYN 61_ IQKES 66_ TLHLV 71_ LRLRG 76_ GMQIF 81_ VKTLT 86_ GKTIT 91_ LEVEP 96_ SDTIE 101_ NVKAK 106_ IQDKE 111_ GIPPD 116_ QQRLI 121_ FAGKQ 126_ LEDGR 131_ TLSDY 136_ NIQKE 141_ STLHL 146_ VLRLR 151_ GGMQI 156_ FVKTL 161_ TGKTI 166_ TLEVE 171_ PSDTI 176_ ENVKA 181_ KIQDK 186_ EGIPP 191_ DQQRL 196_ IFAGK 201_ QLEDG 206_ RTLSD 211_ YNIQK 216_ ESTLH 221_LVLRL
1: 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