RanBP-type and C3HC4-type zinc finger-containing protein 1 (also known as HOIL-1) is a protein that in humans is encoded by the RBCK1 gene. [5]
The protein encoded by this gene is similar to mouse UIP28/UbcM4 interacting protein. Alternative splicing has been observed at this locus, resulting in distinct isoforms. [5]
HOIL-1 is an E3 ubiquitin ligase and a part of the linear ubiquitin chain assembly complex (LUBAC), the only known ubiquitin ligase generating linear (Met1) polyubiquitin linkages. [6] Although HOIL-1 isn’t responsible for the linear ubiquitin generation, it is a necessary component of LUBAC and ensures its proper assembly and function. [7] Interestingly, unlike most E3 ubiquitin ligases, HOIL-1 is able to catalyze oxyester bond formation between the C-terminus of a ubiquitin monomer and Ser/Thr of a different protein. This recently discovered function of HOIL-1 has so far been described in the context of MyD88 signaling. [8] Additionally, a catalytically inactive mutant of HOIL-1 (HOIL-1C458S) led to prolonged IKK activation and increase of inflammatory cytokine production by cytotoxic T cells. The proposed mechanism is that the ester-linked ubiquitin chains limit the size of isopeptide-linked (K63 and/or M1) ubiquitin chains. [9]
A family quartet was found with two children, both affected with a previously unreported disease, characterized by progressive muscular weakness and cardiomyopathy, with normal intelligence. During the course of the study, one additional unrelated patient was found with a comparable phenotype. From whole-genome sequence data, RBCK1, a gene encoding an E3 ubiquitin-protein ligase, was identified as the most likely candidate gene, with two protein-truncating mutations in probands in the first family. Sanger sequencing identified a private homozygous splice variant in RBCK1 in the proband in the second family, yet single-nucleotide polymorphism (SNP) genotyping revealed a 1.2Mb copy-neutral region of homozygosity covering RBCK1. RNA-Seq confirmed aberrant splicing of RBCK1 transcripts, resulting in truncated protein products. [10] Ten other individuals with mutations in RBCK1 and overlapping phenotypes have been identified. [11]
Ubiquitin-protein ligase E3A (UBE3A) also known as E6AP ubiquitin-protein ligase (E6AP) is an enzyme that in humans is encoded by the UBE3A gene. This enzyme is involved in targeting proteins for degradation within cells.
DNA damage-binding protein 1 is a protein that in humans is encoded by the DDB1 gene.
E3 ubiquitin-protein ligase CHFR is an enzyme that in humans is encoded by the CHFR gene.
E3 ubiquitin-protein ligase SMURF1 is an enzyme that in humans is encoded by the SMURF1 gene. The SMURF1 Gene encodes a protein with a size of 757 amino acids and the molecular mass of this protein is 86114 Da.
Cyclin-dependent kinases regulatory subunit 1 is a protein that in humans is encoded by the CKS1B gene.
COP9 signalosome complex subunit 4 is a protein that in humans is encoded by the COPS4 gene.
RING-box protein 2 is a protein that in humans is encoded by the RNF7 gene.
E3 ubiquitin-protein ligase HUWE1 is an enzyme that in humans is encoded by the HUWE1 gene.
NEDD4-like E3 ubiquitin-protein ligase WWP1 is an enzyme that in humans is encoded by the WWP1 gene.
Tripartite motif-containing protein 37 is an E3 ubiquitin ligase in humans that is encoded by the TRIM37 gene.
Ubiquitin/ISG15-conjugating enzyme E2 L6 is a protein that in humans is encoded by the UBE2L6 gene.
The human gene UBR1 encodes the enzyme ubiquitin-protein ligase E3 component n-recognin 1.
Ubiquitin-conjugating enzyme E2 H is a protein that in humans is encoded by the UBE2H gene.
Probable E3 ubiquitin-protein ligase HERC1 is an enzyme that in humans is encoded by the HERC1 gene.
E3 ubiquitin-protein ligase NRDP1 is an enzyme that in humans is encoded by the RNF41 gene.
Tripartite motif-containing protein 32 is a protein that in humans is encoded by the TRIM32 gene. Since its discovery in 1995, TRIM32 has been shown to be implicated in a number of diverse biological pathways.
E3 ubiquitin-protein ligase MARCH7 is an enzyme that in humans is encoded by the MARCH7 gene.
E3 ubiquitin-protein ligase MARCH5, also known as membrane-associated ring finger (C3HC4) 5, is an enzyme that, in humans, is encoded by the MARCH5 gene. It is localized in the mitochondrial outer membrane and has four transmembrane domains.
RNF144A is an E3 ubiquitin ligase belonging to the RING-between RING (RBR) family of ubiquitin ligases, whose specific members have been shown to function as RING-HECT hybrid E3 ligases. RNF144A is most closely related to RNF144B at the protein level, and the two proteins together comprise a subdomain within the RBR family of proteins. The ubiquitin ligase activity of RNF144A catalyzes ubiquitin linkages at the K6-, K11- and K48- positions of ubiquitin in vitro, and is regulated by self-association through its transmembrane domain.
Linear ubiquitin chain assembly complex (LUBAC) is a multi-protein complex and the only known E3 ubiquitin ligase able to conjugate ubiquitin in a head-to-tail manner to generate linear (M1-linked) polyubiquitin chains. The complex is currently known to be composed of three proteins: heme-oxidized IRP2 ubiquitin ligase 1 (HOIL-1), HOIL-1-interacting protein (HOIP), and Shank-associated RH domain-interacting protein (SHARPIN),,. HOIL-1 and HOIP are both E3 ubiquitin ligases, however, the specific linear ubiquitin-ligating activity is enacted by HOIP. Mice deficient in HOIP are embryonically lethal. Two cases of mutated HOIP have been detected in humans. These patients presented with autoinflammation and immunodeficiency,. HOIL-1 is required for LUBAC assembly and stability as demonstrated by embryonic lethality in HOIL-1 deficient mice. Recently, it has been noted, that HOIL-1 is also able to catalyze formation of oxyester bonds between the C-terminus of ubiquitin and serine/threonine of substrate protein in TLR signaling. SHARPIN exhibits a significant sequence similarity to HOIL-1 and is important for LUBAC stability. Spontaneous point mutation in the Sharpin gene in mice leads to development of chronic proliferative dermatitis (cpdm),. Both HOIL-1 and SHARPIN bind to HOIP through their ubiquitin-like (UBL) domain,. LUBAC consisting of either HOIP-HOIL-1 or HOIP-SHARPIN is functional in vitro, however the greatest activity of the complex has been observed in the presence of all three components.