Proteases represent the class of enzymes which occupy a pivotal position with respect to their physiological roles as well as their commercial applications. They perform both degradative and synthetic functions. Since they are physiologically necessary for living organisms, proteases occur ubiquitously in a wide diversity of sources such as plants, animals, and microorganisms. Microbes are an attractive source of proteases owing to the limited space required for their cultivation and their ready susceptibility to genetic manipulation. Proteases are divided into exo- and endopeptidases based on their action at or away from the termini, respectively. They are also classified as serine proteases, aspartic proteases, cysteine proteases, and metalloproteases depending on the nature of the functional group at the active site. Proteases play a critical role in many physiological and pathophysiological processes. Based on their classification, four different types of catalytic mechanisms are operative. Proteases find extensive applications in the food and dairy industries. Alkaline proteases hold a great potential for application in the detergent and leather industries due to the increasing trend to develop environmentally friendly technologies. There is a renaissance of interest in using proteolytic enzymes as targets for developing therapeutic agents. Protease genes from several bacteria, fungi, and viruses have been cloned and sequenced with the prime aims of (i) overproduction of the enzyme by gene amplification, (ii) delineation of the role of the enzyme in pathogenecity, and (iii) alteration in enzyme properties to suit its commercial application. Protein engineering techniques have been exploited to obtain proteases which show unique specificity and/or enhanced stability at high temperature or pH or in the presence of detergents and to understand the structure-function relationships of the enzyme. Protein sequences of acidic, alkaline, and neutral proteases from diverse origins have been analyzed with the aim of studying their evolutionary relationships. Despite the extensive research on several aspects of proteases, there is a paucity of knowledge about the roles that govern the diverse specificity of these enzymes. Deciphering these secrets would enable us to exploit proteases for their applications in biotechnology.

Molecular and Biotechnological Aspects of Microbial Proteases

The type I interferon response protects cells against invading viral pathogens. The cellular factors that mediate this defence are the products of interferon-stimulated genes (ISGs). Although hundreds of ISGs have been identified since their discovery more than 25 years ago, only a few have been characterized with respect to antiviral activity. For most ISG products, little is known about their antiviral potential, their target specificity and their mechanisms of action. Using an overexpression screening approach, here we show that different viruses are targeted by unique sets of ISGs. We find that each viral species is susceptible to multiple antiviral genes, which together encompass a range of inhibitory activities. To conduct the screen, more than 380 human ISGs were tested for their ability to inhibit the replication of several important human and animal viruses, including hepatitis C virus, yellow fever virus, West Nile virus, chikungunya virus, Venezuelan equine encephalitis virus and human immunodeficiency virus type-1. Broadly acting effectors included IRF1, C6orf150 (also known as MB21D1), HPSE, RIG-I (also known as DDX58), MDA5 (also known as IFIH1) and IFITM3, whereas more targeted antiviral specificity was observed with DDX60, IFI44L, IFI6, IFITM2, MAP3K14, MOV10, NAMPT (also known as PBEF1), OASL, RTP4, TREX1 and UNC84B (also known as SUN2). Combined expression of pairs of ISGs showed additive antiviral effects similar to those of moderate type I interferon doses. Mechanistic studies uncovered a common theme of translational inhibition for numerous effectors. Several ISGs, including ADAR, FAM46C, LY6E and MCOLN2, enhanced the replication of certain viruses, highlighting another layer of complexity in the highly pleiotropic type I interferon system.

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A diverse range of gene products are effectors of the type I interferon antiviral response

The mechanism of action of Bcl-2 provides clues for therapeutic interventions

The proto-oncogene Bcl-2 and its role in regulating apoptosis

The JAK-STAT pathway at twenty.

Interferon-stimulated genes and their antiviral effector functions.

Expression of the human immunodeficiency virus type 1 (HIV) protease in cultured cells leads to apoptosis, preceded by cleavage of bcl-2, a key negative regulator of cell death. In contrast, a high level of bcl-2 protects cells in vitro and in vivo from the viral protease and prevents cell death following HIV infection of human lymphocytes, while reducing the yields of viral structural proteins, infectivity, and tumor necrosis factor alpha. We present a model for HIV replication in which the viral protease depletes the infected cells of bcl-2, leading to oxidative stress-dependent activation of NF kappa B, a cellular factor required for HIV transcription, and ultimately to cell death. Purified bcl-2 is cleaved by HIV protease between phenylalanine 112 and alanine 113. The results suggest a new option for HIV gene therapy; bcl-2 muteins that have noncleavable alterations surrounding the HIV protease cleavage site.

https://www.pnas.org/content/pnas/93/18/9571.full.pdf

Apoptosis mediated by HIV protease is preceded by cleavage of Bcl-2

The purification of human fibroblast interferon has been simplified to a two-step procedure consisting of affinity chromatography on Blue Sepharose and sodium dodecyl sulfate polyacrlamide gel electrophoresis. A preliminary amino acid composition and the sequence of the 13 amino-terminal residues of homogeneous interferon prepared by this method is reported.

https://science.sciencemag.org/content/sci/207/4430/525.full.pdf

Human fibroblast interferon: amino acid analysis and amino terminal amino acid sequence

The rate of attachment of type 2 virions to suspensions of HeLa cells is much greater than that of type 14, but the number of receptor sites per cell is similar for each type. The receptor sites may be partly saturated with excess virions; attachment is greatly reduced after about 104 particles have been taken up per cell. A lack of saturation of type 14 receptors by excess type 2 indicates that their receptor sites are separate on the cell surface. Excess of type 2 blocks attachment of type 1A, however, and excess of type 14 blocks type 51. Attachment of the human rhinoviruses is temperature-dependent with a Q10 of 2.7. The eclipse reaction is also temperature-dependent. At 34.5 C, the irreversible eclipse of cell-associated rhinovirus type 2 requires only a few minutes, whereas the rate of eclipse of cell-associated type 14 is considerably slower. The eclipse product of type 2 rhinovirus has been recovered from infected cells. It sediments at about 90% of the rate of the infective virions and is missing virus polypeptide 4 (the smallest of the capsid polypeptides). Upon being subjected to CsCl gradient centrifugation, virus polypeptide 2 is also lost but the product still contains ribonucleic acid and bands at about 1.45 g/cc.

Bruce D. Korant

Papers

Apoptosis mediated by HIV protease is preceded by cleavage of Bcl-2

Human fibroblast interferon: amino acid analysis and amino terminal amino acid sequence

Early Interaction of Rhinoviruses with Host Cells

Naturally occurring and artificially produced components of three rhinoviruses.

Cystatin, a protein inhibitor of cysteine proteases alters viral protein cleavages in infected human cells.