A Brief Note On Interferons

2.1 Interferon-γ
2.1.1 Introduction
Interferons are the family of cytokine whose primary role is to inhibit the viral infection and intracellular bacterial infection and also tumor control (Ebrahimi et al., 2012). Interferons are classified into two types based on receptor binding and sequence homology. Primary role of type I interferon (IFN- α, IFN- β, IFN- ω, IFN-τ) is to make cells resistant to viral infections and type II interferon (IFN-γ) is to regulate overall immune response (Schroder et al., 2004).
IFN-γ is a secretory glycosylated protein of total molecular weight of 25kDa. It is a major cytokine which regulate both innate and adaptive immunity (Savana et al., 2009). IFN-γ is secreted by CD4+ T helper cells type 1 (Th1) lymphocytes, CD8+T cytotoxic lymphocytes, NK cells and NKT cells and also by antigen presenting cells like macrophages, dendritic cells and B lymphocytes (McLaren and Ramji, 2009). IFN-γ production is further stimulated by the combination of Interleukin-12 (IL-12) and Interleukin-18 (IL-18), whereas it is negatively regulated by Interleukin-4 (IL-4), Interleukin-10 (IL-10), growth promoting factor- β, glucocorticoids (Schroder et al., 2004). IL-12 promotes differentiation of naive CD4+ T cells to Th1 cells, which produce IFN- γ and augment cell mediated immune response (O'Shea et al., 2002).

2.1.2 Gene Structure
IFN-γ gene is located on the human chromosome 12 of gene size 501bp (Bureau et al., 1995). Unlike IFN-α and IFN-β, IFN-γ has no introns (Taya et al., 1982).
2.1.3 Protein structure
IFN-γ is homo-dimer glycoprotein (Savana et al., 2009), of 166 amino acids, in which 20 N-terminal sequence act as signal peptides (Taya et al., 1982). It has two subunits and each subunit has 6 alpha helices held tog...

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...Drocourt et al., 1990).
2.2.5 Signal sequence
The heterologous preprot signal sequence (269bp) of the S. cerevisiae alpha-mating factor is most often used to induce Sec61p-mediated translocation of the protein into the endoplasmic reticulum of P. pastoris. The Kex2p/Ste13p-mediated processing of the propeptide in this S. cerevisiae sequence is often problematic in P. pastoris, resulting in the production of different amino acids at the N-terminus of the heterologous protein (De Schutter et al., 2009). The processing of the α-factor secretion signal sequence in pPICZα A occurs in two steps namely the preliminary cleavage of the signal sequence by the KEX2 gene product, with the final KEX2 cleavage occurring between arginine and glutamine in the sequence Glu-Lys-Arg-Glu-Ala-Glu-Ala. The Glu-Ala repeats are further cleaved by STE13 gene product (Brake et al., 1984).