Suppressor of cytokine signalling (SOCS) proteins form part of a classical negative feedback system that regulates cytokine signal transduction. SOCS5 inhibits the IL4 signaling pathway, which promotes the Th (helper T) 2 cell development []. SOCS5 and SOCS4 regulate epidermal growth factor receptor signaling [].
This entry represents the SOCS box domain of SOCS5.Suppressor of cytokine signalling (SOCS) proteins form part of a classical negative feedback system that regulates cytokine signal transduction. SOCS5 inhibits the IL4 signaling pathway, which promotes the Th (helper T) 2 cell development []. SOCS5 and SOCS4 regulate epidermal growth factor receptor signaling [].The general function of the SOCS box is the recruitment of the ubiquitin-transferase system. The SOCS box interacts with Elongins B and C, Cullin-5 or Cullin-2, Rbx-1, and E2. Therefore, SOCS-box-containing proteins probably function as E3 ubiquitin ligases and mediate the degradation of proteins associated through their N-terminal regions [, ].
The Btk-type zinc finger or Btk motif (BM) is a conserved zinc-binding motif containing conserved cysteines and a histidine that is present in certain eukaryotic signalling proteins. The motif is named after Bruton's tyrosine kinase (Btk), an enzyme which is essential for B cell maturation in humans and mice [, ]. Btk is a member of the Tec family of protein tyrosine kinases (PTK). These kinases contain a conserved Tec homology (TH) domain between the N-terminal pleckstrin homology (PH) domain () and the Src homology 3 (SH3) domain (). The N-terminal of the TH domain is highly conserved and known as the Btf motif, while the C-terminal region of the TH domain contains a proline-rich region (PRR). The Btk motif contains a conserved His and three Cys residues that form a zinc finger (although these differ from known zinc finger topologies), while PRRs are commonly involved in protein-protein interactions, including interactions with G proteins [, ]. The TH domain may be of functional importance in various signalling pathways in different species []. A complete TH domain, containing both the Btk and PRR regions, has not been found outside the Tec family; however, the Btk motif on its own does occur in other proteins, usually C-terminal to a PH domain (note that although a Btk motif always occurs C-terminal to a PH domain, not all PH domains are followed by a Btk motif).The crystal structures of Btk show that the Btk-type zinc finger has a globular core, formed by a long loop which is held together by a zinc ion, and that the Btk motif is packed against the PH domain []. The zinc-binding residues are a histidine and three cysteines, which are fully conserved in the Btk motif []. Proteins known to contain a Btk-type zinc finger include:Mammalian Bruton's tyrosine kinase (Btk), a protein tyrosine kinase involved in modulation of diverse cellular processes. Mutations affecting Btk are the cause of X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency in mice. Mammalian Tec, Bmx, and Itk proteins, which are tyrosine protein kinases of the Tec subfamily. Drosophila tyrosine-protein kinase Btk29A, which is required for the development of proper ring canals and of male genitalia and required for adult survival. Mammalian Ras GTPase-activating proteins (RasGAP), which regulate the activation of inactive GDP-bound Ras by converting GDP to GTP.
Txk is a member of the Tec protein tyrosine kinase family. It plays a role in TCR signal transduction, T cell development, and selection which is analogous to the function of Itk. Txk has been shown to interact with IFN-gamma [, ]. Unlike most of the Tec family members Txk lacks a PH domain. Instead Txk has a unique region containing a palmitoylated cysteine string which has a similar membrane tethering function as the PH domain []. This entry includes the SH2 domain of Txk.The Tec protein tyrosine kinase family includes Tec,Btk, Itk, Bmx, and Txk. They contain an NH2-terminal pleckstrin homology (PH) domain (absent in Txk), a proline-rich region, Src-homology 3 (SH3) and SH2 domains, and a COOH-terminal PTK domain. The TH domain consists of a Zn2+-binding Btk motif and a proline-rich region. The Btk motif is found in Tec kinases, Ras GAP, and IGBP and crucial to the function of the PH domain. It is not present in Txk which is not surprising since it lacks a PH domain. The type 1 splice form of the Drosophila homologue also lacks both the PH domain and the Btk motif. The proline-rich regions are highly conserved for the most part with the exception of Bmx whose residues surrounding the PXXP motif are not conserved (TH-like) and Btk29A which is entirely unique with large numbers of glycine residues (TH-extended). Tec family members all lack a C-terminal tyrosine having an autoinhibitory function in its phosphorylated state [, ].
Apoptosis signal-regulating kinases (ASK1/2/3 or MAP3K5/6/15) are mitogen-activated protein kinase kinase kinases (MAP3Ks) that mediate cellular responses to redox stress and inflammatory cytokines and play a key role in innate immunity and viral infection. This kind of signalling kinases are regulated by oligomerization and regulatory domains. In its N-terminal there is a thioredoxin-binding domain that negatively regulates activity and a TNF receptor-associated factors (TRAFs)-binding domain which triggers ASK activation and kinase activity. TRAFs-binding domain is composed by 14 helices, which form seven tetratricopeptide repeats (TPRs), followed by a PH-like domain to complete de central regulatory domain of ASK. The central regulatory region promotes ASK1 activity via its PH domain but also facilitates ASK1 autoinhibition by bringing the thioredoxin-binding and kinase domains into close proximity. The PH-like domain, adjacent to the kinase domain, is required together with an intact TPR region for ASK1 activity.The major role of the central regulatory region is to bring the thioredoxin-binding domain into close proximity to the kinase domain to inhibit its activity [].This domain corresponds to the TRAFs-binding domain found at the N terminus of some MAP3Ks. This domain includes seven tetratricopeptide repeats (TPRs) and, together with th PH-like domain, constitutes the central regulatory domain of ASK1.
Th SWR1 complex is involved in chromatin-remodelling by promoting the the ATP-dependent exchange of histone H2A for the H2A variant HZT1 in Saccharomyces cerevisiae (Baker's yeast) or H2AZ in mammals. The SWR1 chromatin-remodelling complex is composed of at least 14 subunits and has a molecular mass of about 1.2 to 1.5 MDa. In S. cerevisiae the core conserved subunits are: ATPase; Swr1.RuvB-like; Rvb1 and Rvb2.Actin; Act1.Actin-related: Arp4 and Arp6.YEATS protein []; Yaf9.The non-conserved subunits are: Vps71 (Swc6), Vps72 (Swc2), Swc3, Swc4, Swc5, Swc7, Bdf1 [].Seven of the SWR1 subunits are involved in maintaining complex integrity and H2AZ histone replacement activity: Swr1, Swc2, Swc3, Arp6, Swc5, Yaf9 and Swc6. Arp4 is required for the association of Bdf1, Yaf9, and Swc4 and Arp4 is also required for SWR1 H2AZ histone replacement activity in vitro. Furthermore the N-terminal region of the ATPase Swr1 provides the platform upon which Bdf1, Swc7, Arp4, Act1, Yaf9 and Swc4 associate []; it also contains an additional H2AZ-H2B specific binding site, distinct from the binding site of the Swc2 subunit []. In eukaryotes the deposition of variant histones into nucleosomes by the chromatin-remodelling complexes such as the SWR1 and INO80 complexes have many crucial functions including the control of gene regulation and expression, checkpoint regulation, DNA replication and repair, telomer maintenance and chromosomal segregation and as such represent critical components of pathways that maintain genomic integrity. This entry represents the subunit Swc7; the smallestsubunit of the SWR1 complex. Swc7 is not required for H2AZ binding. Swc7 associates with the N terminus of Swr1, and the association of Bdf1 requires Swc7, Yaf9, and Arp4 [].
