ubiquitin (UBCEP2, UBB, UBC)

Introduction

A non-histone high mobility group protein found in chromatin.

Function

• derived from cleavage of ribosomal protein S27A
• adenylate cyclase stimulating polypeptide
• covalently attached to target proteins by a multienzymatic system consisting of:
  • ubiquitin-activating enzyme E1
  • ubiquitin-conjugating enzyme E2
  • ubiquitin-ligating enzyme E3
• ubiquitin is attached to Lys on the target protein as a monomer or as a Lys-linked polymer
• the 26S proteasome is involved in ubiquitin-mediated degradation of proteins
• attachment to proteins as a Lys-48-linked polymer usually leads to their degradation by proteasome
• attachment to proteins as a Lys-63-linked polymer usually does NOT lead to their degradation, but are rather plays a role in signaling cellular stress
• single chain of at least 4 ubiquitin residues attached to a single Lys is necessary for ubiquitin-mediated proteolysis
• attachment to proteins as a monomer or as an alternatively linked polymer does not lead to proteasomal degradation & may be required for numerous functions, including
  • maintenance of chromatin structure
  • regulation of gene expression
  • stress response
  • ribosome biogenesis
  • DNA repair
• several types of polymeric chains can be formed, depending on the Lys used for the assembly

Structure

• the last four C-terminal residues (Leu-Arg-Gly-Gly) extending from the compact structure of ubiquitin to form a 'tail' involved in covalent conjugation of ubiquitin to target proteins
• ubiquitin conjugation occurs through an isopeptide linkage between the C-terminal Gly of ubiquitin & the epsilon amino group of Lys in the target proteins
• ubiquitin is synthesized as a polyubiquitin precursor with exact head to tail repeats
• belongs to the ubiquitin family

Compartment

cytoplasm, nucleus

Comparative biology

• believed to be universal in all living cells
• the number of repeats differ between species & strains
• in some species there is a final amino-acid after the last repeat, here in human a Val
• some ubiquitin genes contain a single copy of ubiquitin fused to a ribosomal protein (either L40 or S27a)

More general terms

• high-mobility group [HMG] protein

More specific terms

• polyubiquitin-B; contains: ubiquitin (UBB)
• polyubiquitin-C; contains: ubiquitin (UBC)

Additional terms

• 26S proteasome
• E3 ubiquitin ligase; ubiquitin-ligating enzyme E3; N end-recognizing protein
• ubiquitin C-terminal hydrolase; UCH; ubiquitin thiolesterase; ubiquitin-specific processing protease; deubiquitinating enzyme
• ubiquitin-activating enzyme E1 (ubiquitin-like modifier-activating enzyme 1, A1S9 protein, UBE1, UBA1, A1S9T)
• ubiquitin-conjugating protein E2 (ubiquitin carrier protein)

Database

• UniProt: http://www.uniprot.org/uniprot/P0CG48.html
• UniProt: http://www.uniprot.org/uniprot/P0CG47.html
• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=7314
• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=7316
• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:7314
• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:7316
• Kegg: http://www.genome.jp/dbget-bin/www_bget?
• OMIM: https://mirror.omim.org/entry/191320
• OMIM: https://mirror.omim.org/entry/191321
• OMIM: https://mirror.omim.org/entry/191339
• OMIM: https://mirror.omim.org/entry/191340
• OMIM: https://mirror.omim.org/entry/191343