Formulation: Lyophilized from sterile 50 mM Tris, pH 8.0
Purity: ≥95% estimated by SDS-PAGE
Shelf life (days): 365
Notes: Interferon-stimulated gene 15 (ISG15) is a ubiquitin-like (Ubl) protein found only in vertebrates.{57855,57856} The mature form of ISG15 is composed of an N-terminal Ubl and a C-terminal Ubl with an LRLRGG conjugation sequence at the C-terminus.{57856} It is expressed in lymphoid cells, epithelial cells, neurons, and skeletal and smooth muscle, and its expression is induced by type I interferon signaling in response to viral or bacterial infection but is also induced in response to the aging process and certain diseases.{57857,57855,57856} ISG15 is primarily localized intracellularly conjugated to lysine residues in newly synthesized proteins via ISGylation, a process that can enhance antiviral responses.{57855} It also exists in a free form that can be secreted by a variety of cells, including fibroblasts, monocytes, and lymphocytes, and binds to the adhesion molecule lymphocyte function-associated antigen-1 (LFA-1) on leukocytes to increase the secretion of IFN-γ. ISG15 can ISGylate viral proteins to prevent viral replication and inhibit the function of viral proteins, however ISGylation on host proteins can be reversed by certain viruses, including severe acute respiratory coronavirus 2 (SARS-CoV-2), leading to suppression of the host innate immune response.{57855,54466,54467} Patients deficient in functional ISG15 due to inherited mutations in ISG15 are more resistant to viral infection, but have an increased susceptibility to mycobacterial infection, while Isg15 knockout mice are more susceptible to viral infection, indicating species-specific differences.{57858,57859} Cayman’s ISG15 (mature form) (human, recombinant) protein consists of 157 amino acids and has a calculated molecular weight of 17.2 kDa. By SDS-PAGE, under reducing conditions, the apparent molecular mass of the protein is 15 kDa.
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