Ailuropoda melanoleuca

    Atg12, a post-translational modifier, which can be activated and conjugated to Atg5 by a ubiquitin-like conjugation system, though it has no obvious sequence homology to ubiquitin. It's carboxyl-terminal that is fold into a ubiquitin-like structure is necessary and sufficient for both conjugation and autophagy (1).

1. Hanada T, Ohsumi Y(2005). Structure-function relationship of Atg12, a ubiquitin-like modifier essential for autophagy. Autophagy., 1(2):110-8. PMID:16874032

    ATG8 family contains ubiquitin-like modifiers that play a role in intracellular transport of GABA(A) receptors and its interaction with the cytoskeleton, as well as ubiquitin-like protein required for autophagy that can be conjugated to the lipid phosphatidylethanolamine by a ubiquitin-like system. These ubiquitin-like proteins involved in apoptosis and autophagy.

    NEDD8 family contains ubiquitin-like protein which plays an important role in cell cycle control and embryogenesis. Attachment of NEDD8 to cullins activates their associated E3 ubiquitin ligase activity, and thus promotes polyubiquitination and proteasomal degradation of cyclins and other regulatory proteins. NEDD8 pathway is essential for SCF(beta -TrCP)-mediated ubiquitination (1).

1. Amir RE, Iwai K, Ciechanover A(2002) The NEDD8 pathway is essential for SCF(beta -TrCP)-mediated ubiquitination and processing of the NF-kappa B precursor p105. J Biol Chem., 277(26):23253-9. PMID:11953428

    Small ubiquitin-related modifier (SUMO) family contains a series of ubiquitin-like proteins, such as SUMO1, SUMO2, SUMO3, SUMO4, SUMO5 and SUMO8. The SUMO protein and ubiquitin have similar 3-D structure. Sumolyzation and ubiquitination exhibit similar biological processes for post-translational modification. However, unlike ubiquitination, which targets proteins for degradation, sumolyzation participates in a number of cellular processes such as nuclear transport, transcriptional regulation, apoptosis and protein stability.

    UBQ_Other family is a collection of unconventional ubiquitin-like domain containing proteins. This family conains proteins that possess similar structure or sequence homology with ubiquitin. ubiquitin-like protein modifier can be covalently attached to target protein and subsequently leads to their degradation by the 26S proteasome.

    The proteasome-interacting motif (PIM) containing UbLDs mostly occur in the N-terminal region of UbLPs. The ubiquitin-like domain binds the subunit of 26S proteasomes.

    The DWNN (Domain With No Name) domain contains ~75 residues, which is highly conserved through eukaryotic species but is absent in prokaryotes (1). The DWNN domain may act as an ubiquitin-like modifier, possibly playing a role in the regulation of the splicing machinery.

1. http://pfam.xfam.org/family/PF08783

    Membrane-anchored Ub-fold(MUBs) is a family of ubiquitin-fold proteins that are plasma membrane-anchored by prenylation.MUB proteins present in animals, filamentous fungi, and plants. Extending from the C terminus of the Ub-fold is typically a cysteine-containing CAAX (where A indicates aliphatic amino acid) sequence that can direct the attachment of either a 15-carbon farnesyl or a 20-carbon geranylgeranyl moiety in vitro (1).

1. Downes BP, Saracco SA, Lee SS, Crowell DN, Vierstra RD (2006). MUBs, a family of ubiquitin-fold proteins that are plasma membrane-anchored by prenylation. Trends in Biochemical Sciences., 281(37):27145-57. PMID:16831869

    The PB1 (Phox and Bem1) domain (1), comprising about 80 amino acid residues, is conserved among animals, fungi, amoebas, and plants. It functions as a protein binding module through PB1-mediated heterodimerization or homo-oligomerization (2).

1. http://pfam.xfam.org/family/PF00564

    The RAWUL domain is found at the C terminus of poly-comb group RING finger proteins. It contains a variant ubiquitin-like fold with a distinct conserved surface region. The conserved surface found in this domain is responsible for interaction with Cbx members of the PRC1 (polycomb repression complex 1) and homodimer formation.

1. http://pfam.xfam.org/family/PF16207

2. Bezsonova I , Walker JR , Bacik JP , Duan S , Dhe-Paganon S , Arrowsmith CH (2009). Ring1B contains a ubiquitin-like docking module for interaction with Cbx proteins. Biochemistry., 48(44):10542-8. PMID:19791798

    The UBX domain shares the same superfold (1), and an evolutionary relationship with ubiquitin (2), and is found in ubiquitin-regulatory proteins, which are members of the ubiquitination pathway. The UBX domain is a widespread ubiquitin-like module. The function of the UBX domain is not known although the fragment of avian FAF-1 containing the UBX domain causes apoptosis of transfected cells.

1. http://pfam.xfam.org/family/PF00789

2. Buchberger A, Howard MJ, Proctor M, Bycroft M. (2001). The UBX domain: a widespread ubiquitin-like module. J Mol Biol., 307(1):17-24. PMID:11243799