Cellular uptake of the tat protein from human immunodeficiency virus

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

https://www.cell.com/cell/pdf/0092-8674(88)90262-0.pdf

Autonomous functional domains of chemically synthesized human immunodeficiency virus tat trans-activator protein.

A series of peptide derivatives based on the transition-state mimetic concept has been designed that inhibit the proteinase from the human immunodeficiency virus (HIV). The more active compounds inhibit both HIV-1 and HIV-2 proteinases in the nanomolar range with little effect at 10 micromolar against the structurally related human aspartic proteinases. Proteolytic cleavage of the HIV-1 gag polyprotein (p55) to the viral structural protein p24 was inhibited in chronically infected CEM cells. Antiviral activity was observed in the nanomolar range (with one compound active below 10 nanomolar) in three different cell systems, as assessed by p24 antigen and syncytium formation. Cytotoxicity was not detected at 10 and 5 micromolar in C8166 and JM cells, respectively, indicating a high therapeutic index for this new class of HIV proteinase inhibitors.

https://science.sciencemag.org/content/sci/248/4953/358.full.pdf

Rational design of peptide-based HIV proteinase inhibitors

The crystal structure of the protease of the human immunodeficiency virus type (HIV-1), which releases structural proteins and enzymes from viral polyprotein products, has been determined to 3 A resolution. Large regions of the protease dimer, including the active site, have structural homology to the family of microbial aspartyl proteases. The structure suggests a mechanism for the autoproteolytic release of protease and a role in the control of virus maturation.

Three-dimensional structure of aspartyl protease from human immunodeficiency virus HIV-1

Human immunodeficiency virus encodes a gene product termed tat that is able to activate viral gene expression when present in trans. The mechanism of action of the tat gene product appears to be bimodal, resulting in both an increase in the steady-state level of viral mRNA and the enhanced translation of that RNA. In this report we have examined the mechanism by which tat elevates viral mRNA levels. Data are presented demonstrating that tat acts by increasing the rate of viral transcription, rather than by modulating the stability of viral mRNA. Indirect immunofluorescence was used to show that tat is predominantly localized in the nucleus of expressing cells, a location consistent with a role in the regulation of viral transcription. These results suggest that tat could play a role in human immunodeficiency virus replication essentially similar to that proposed for the trans-acting nuclear gene products described for several other virus species.

https://www.pnas.org/content/pnas/84/18/6364.full.pdf

Trans-activation of human immunodeficiency virus gene expression is mediated by nuclear events

(6) H. Hagenmaier and M. Mutter, Tetrahedron Lett., 767-770 (1974). (7) W. Gohring and G. Jung, Justus Liebigs Ann. Chern., 1765-1789 (1975). (8) M. Mutter, R. Uhmann, and E. Bayer, Justus Liebigs Ann. Chern., 901-915 ( 1975). (9) G. Jung, G. Bovermann, W. Gohring, and G. Heusel in "Peptides: Chemistry, Structure and Biology," R. Walter and J. Meienhofer, Ed., Ann Arbor Sci. Publ., Ann Arbor, Mich., 1975, pp 433-437. (10) F A . Tjoeng, W Staines, S. St-Pierre, and R. S. Hodges, Biochirn. Biophys. Acta, 490, 489-496 (1977). (1975). (1 1) L. B. Smillie, PAABS Revista, 5, 183-263 (1976). (12) R. S. Hodges, J. Sodek, L. B. Smillie, and L. Jurasek, ColdSpring Harbor

http://www.sciencemadness.org/talk/files.php?pid=116909&aid=4738

Rapid removal of protecting groups from peptides by catalytic transfer hydrogenation with 1,4-cyclohexadiene

/pdf/by-plasma-in-vitro-and-in-vivo-to-a-biologically-inactive-r7ynygykvc.pdf

by Plasma In Vitro and In Vivo to a Biologically Inactive Product Cleaved at the NH2 Terminus

In order to define the protease domain of human immunodeficiency virus 1, various regions of the pol open reading frame were cloned and expressed in Escherichia coli. Antiserum directed against the conserved retroviral protease active site was used to identify pol precursor and processed species containing the presumed protease domain. The smallest product that accumulates is about 11 kDa as measured by NaDodSO4/PAGE. This size agrees with that predicted from the presence in this region of two Phe-Pro sequences, which is one of the cleavage sites recognized by HIV protease. DNA encoding only the predicted 11-kDa protein was cloned, bypassing the need for autoprocessing, and the protein was expressed to a high level in E. coli. This form is active as demonstrated by its ability to specifically cleave protease-deficient pol protein in vivo in E. coli. Extracts of E. coli containing the 11-kDa protease also process human immunodeficiency virus gag substrates in vitro. These results demonstrate that the 11-kDa protease is sufficient for enzymatic activity and are consistent with a major role for this form in virus maturation.

Edgar P. Heimer

Papers

Trans-activation of human immunodeficiency virus gene expression is mediated by nuclear events

Rapid removal of protecting groups from peptides by catalytic transfer hydrogenation with 1,4-cyclohexadiene

by Plasma In Vitro and In Vivo to a Biologically Inactive Product Cleaved at the NH2 Terminus

An 11-kDa form of human immunodeficiency virus protease expressed in Escherichia coli is sufficient for enzymatic activity

Defining minimal requirements for antibody production to peptide antigens.