Isopentenyl Pyrophosphate Isomerase 2 (IDI2) belongs to the IPP isomerase type 1 family. Both isozymes, IDI1 and IDI2 are localized to the peroxisome by a PTS1-dependent pathway. IDI2 is expressed in skeletal muscle, which contains one nudix hydrolase domain. IDI2 binds one magnesium per subunit. IDI2 catalyzes the 1,3-allylic rearrangement of the homoallylic substrate isopentenyl (IPP) to its highly electrophilic allylic isomer, dimethylallyl diphosphate (DMAPP). It is reported that IDI2 is regulated independently from IDI1, by a mechanism that may involve PPAR-α.
Parathyroid hormone is the most important endocrine regulator of calcium and phosphorus concentration in extracellular fluid. This hormone is secreted from cells of the parathyroid glands and finds its major target cells in bone and kidney. Another hormone, parathyroid hormone-related protein, binds to the same receptor as parathyroid hormone and has major effects on development. Like most other protein hormones, parathyroid hormone is synthesized as a preprohormone. After intracellular processing, the mature hormone is packaged within the Golgi into secretory vesicles, the secreted into blood by exocytosis. Parathyroid hormone is secreted as a linear protein of 84 amino acids.
Interleukin-1 receptor-associated kinase 4, also known as Renal carcinoma antigen NY-REN-64, IRAK-4 and IRAK4, is a member of the protein kinase superfamily, TKL Ser/Thr protein kinase family and Pelle subfamily. IRAK4 contains onedeath domain and oneprotein kinase domain. IRAK4 is required for the efficient recruitment of IRAK1 to the IL-1 receptor complex following IL-1 engagement, triggering intracellular signaling cascades leading to transcriptional up-regulation and mRNA stabilization. It also phosphorylates IRAK1. A member of the IL-1 receptor (IL-1R)-associated kinase (IRAK) family, IRAK4, has been shown to play an essential role in Toll-like receptor (TLR)-mediated signaling. IL-1-mediated IRAK4 kinase activity in T cells is essential for induction of IL-23R expression, Th17 differentiation, and autoimmune disease. Pharmacological blocking of IRAK4 kinase activity will retain some levels of host defence, while reducing the levels and duration of inflammatory responses, which should provide beneficial therapies for sepsis and chronic inflammatory diseases. Defects in IRAK4 are the cause of recurrent isolated invasive pneumococcal disease type 1 (IPD1) which is defined as two episodes of IPD occurring at least 1 month apart, whether caused by the same or different serotypes or strains. Recurrent IPD occurs in at least 2% of patients in most series, making IPD the most important known risk factor for subsequent IPD. Defects in IRAK4 are also the cause of IRAK4 deficiency which causes extracellular pyogenic bacterial and fungal infections in otherwise healthy children.
Interferon Regulatory Factor 5 (IRF5) is a member of the IRF family. It contains one IRF tryptophan pentad repeat DNA-binding domain. IRF5 shuttles between the nucleus and the cytoplasm. IRF5 can form homodimer when it is phosphorylated. IRF5 functions as a transcription factor involved in the induction of interferons IFNA and INFB and inflammatory cytokines upon virus infection. Genetic variations in IRF5 are associated with susceptibility to systemic lupus erythematosus type 10. In addition, the genetic variations wil result in susceptibility to rheumatoid arthritis.
Interferon-induced 17 kDa protein (ISG15), a 15-kDa protein of unique primary amino acid sequence, functions intracellularly as an ubiquitin homologue and a cytokine that induces production of IFN-gamma and augments NK / lymphokine-activated killer cell proliferation and function. ISG15 is secreted from monocytes and lymphocytes. ISG15 is an ubiquitin-like molecule that is strongly upregulated by type I interferons as a primary response to diverse microbial and cellular stress stimuli. Alterations in the ISG15 signalling pathway have also been found in several human tumour entities. In addition to being stimulated by type I interferon, expression of ISG15 is greatly induced by viral or bacterial infection through the Janus kinase / signal transducer and activator of transcription (Jak / STAT) signalling pathway. After induction, ISG15 is secreted by monocytes, B- and T-lymphocytes and fibroblasts. We demonstrate the novel way in which the function of the ISG15 protein is inhibited by influenza B virus, which strongly induces the ISG15 protein: a specific region of the influenza B virus NS1 protein, which includes part of its effector domain, blocks the covalent linkage of ISG15 to its target proteins both in vitro and in infected cells.
Ubiquitin-Like Protein ISG15 (ISG15) is a ubiquitin-like protein that becomes conjugated to many cellular proteins upon activation by interferon-alpha and -beta. Several functions have been ascribed to the encoded protein, including chemotactic activity towards neutrophils, direction of ligated target proteins to intermediate filaments, cell-to-cell signaling, and antiviral activity during viral infections. While conjugates of this protein have been found to be noncovalently attached to intermediate filaments, this protein is sometimes secreted. ISG15 becomes conjugated to a diverse set of proteins after IFN-alpha/beta stimulation or microbial challenge. The functions or biochemical consequences ISG15 conjugation to proteins are not yet known, but it appears that this modification does not target proteins for proteasomal degradation. ISG15 shows specific chemotactic activity towards neutrophils and activates them to induce release of eosinophil chemotactic factors. Upon interferon treatment, ISG15 can be detected in both free and conjugated forms, and is secreted from monocytes and lymphocytes where it can function as a cytokine. In the cell, ISG15 co-localizes with intermediate filaments and ISGylation may modulate the JAK-STAT pathway or certain aspects of neurological disease.
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