User:HopeBarnum/toxic shock syndrome toxin

=Project Proposal=

Introduction
A brief introduction expanding on the one already present in the article

Characteristics
Toxic Shock Syndrome Toxin (TSST-1), a prototype superantigen induced by a Staphylococcus aureus bacterium strain in susceptible hosts, acts on the vascular system by causing inflammation, fever, and shock. TSST-1 is a bacterial exotoxin that with a single polypeptide chain. The structure of TSST-1 is three-dimensional and consists of an alpha (α) and beta (β) domain. The two domains are adjacent from each other and possess unique qualities. Domain A is long alpha (α) helix surrounded by a 5-strand beta (β) sheet. Domain B is unique because it consists of (β) barrel made up of 5 β-strands. Crystallography methods show that the internal β-barrel of Domain B contains several hydrophobic amino acids and hydrophilic residues on the surface of the Domain, which allows TSST-1 to the cross mucous surfaces of epithelial cells. TSST-1 can be found in men, women, children, and even non-menstruating women. Staphylococcus aureus bacteria that produces the TSST-1's in any area of the body, live mostly in the vagina of infected women. One-third of all Toxic Shock Syndrome (TSS) cases however, are found in men. This statistic could possibly be due to surgical wounds or any skin wound

Production
TSST-1 is a protein encoded by the tstH gene, which is part of a mobile genetic element in the bacterial genome. TSST-1 differs from other superantigens in that its genetic sequence does not have a homolog with other superantigen sequences. When the protein is translated, it is in a pro-protein form, and can only leave the cell once a signal sequence has been cleaved off. It also appears that the superantigenic and lethal portions of the protein are separate, based on studies of various mutations of the protein.

Purification
Samples of TSST-1 can be purified from bacterial cultures to use in in vitro testing environments, however this is not ideal due to the large number of factors that contribute to pathenogenesis in an in vivo environment. Additionally, culturing bacteria in vitro provides an environment which is rich in nutrients, in contrast to the reality of an in vivo environment, in which nutrients tend to be more scarce.

Mechanism
A superantigen such as TSST-1 stimulates human T cells that express VB 2, which may represent 5-30 % of all host T cells, PSTAgs induce the VB-specific expansion of both CD4 and CD8- subsets of T Lymphocytes. TSST-1 forms homodimers in most of it's known crystal forms. The SAGs show remarkably conserved architecture and are divided into the N- and C- terminal domains. TSST-1 binds primarily to the alpha-chain of class II MHC exclusively through a low-affinity (or generic) binding site on the SAG N-terminal domain. This is opposed to other super antigens (SAGs) such as DEA and SEE, that bind to class II MHC through the low-affinity site, and to the beta-chain through a high-affinity site. This high-affinity site is a zinc-dependent site on the SAG C-terminal domain. When this site is bound, it extends over part of the binding groove, makes contacts with the bound peptide,and then binds regions of both the alpha and beta chains. MHC-binding by TSST-1 is partially peptide-dependent. Mutagenesis studies with SEA have indicated that both binding sites are required for optimal T-cell activation. These studies containing TSST-1 indicate that the TCR binding domain lies at the top of the back side of this toxin, though the complete interaction remains to be determined. There have also been indications that the TCR binding site of TSST-1 is mapped to the major groove of the central alpha helix or the short amino terminal alhpha helix. Residues in the beta claw motif of TSST-1 are known to interact primarily with the invariant region of the Alpha chain of this MHC class II molecule. Residues also forming minor contacts with TSST-1 were also identified in the HLA-DR1 β-chain, as well as the antigenic peptide, located in the interchain groove. The arrangement of TSST-1 with respect to the MHC class II molecule imposes steric restriction on the three component complex composed of TSST-1, MHC class II, and the TCR. Mutational analysis has mapped the putative TCR binding region of TSST-1 to a sire located on the back-side groove. If the TCR occupies this sit, the amino terminal alpha helix forms a large wedge between the TCR and MHC class II molecules. The wedge would physically separate the TCR from the MHC class II molecules. A novel domain may exist in the SAGs that is separate from the TCR and class II MHC-binding domains. The domain consists of residues 150 to 161 in SEB, and similar regions exist in all the other SAGs as well. In this study a synthetic peptide containing this sequence was able to prevent SAG-induced lethality in D-galactosamine-sensitized mice with staphylcoccal TSST-1, as well as some other SAGs. Significant differences exist in the sequences of MHC Class II alleles and TCR Vbeta elements expressed by different species, and these differences have important effects on the interaction of PSTAgs and with MCH class II and TCR molecules. Intitial studies of mutants revealed that residues on the back side of the central alpha helix were required for super antigenic activity. Changing the histidine at position 135 to alanine caused TSST-1 to be neither lethal or superantigenic. Changes in residues that were in close proximity to H135A, also had the effect of diminishing the lethality and superantigenic quality of these mutants. Although most of these mutants did not result in loss of antigenicity of TSST-1. Tests done using mutagenic TSST-1 toxins indicated that the lethal and superantigenic properties are separable. When Lys-132 in TSST-O was changed to a Glu, the resulting mutant became completely lethal but non superantigenic. The same results ,lethal but not superantigenic, were found for TSST-1 Gly16Val. Residues Gly16, Glu132,and Gln 136, located on the back of the back-side groove of the putative TCR binding region of TSST-1, it has been proposed that they are also apart of a second functionally lethal site in the TSST-1.

Division of Labor

 * Hope will be responsible for expanding production and purification
 * Britney will be responsible for expanding characteristics
 * Emily will be responsible for expanding mechanism
 * All group members will contribute to formatting/reformatting as needed