Structure
In the nucleotide sequence of TSST-1, there is a 708 base-pair open-reading frame and a Shine-Delgarno sequence which is seven base pairs downstream from the start site. In the entire nucleotide sequence, only 40 amino acids make up the signal peptide. A single signal peptide consists of a 1 to 3 basic amino acid terminus, a hydrophobic region of 15 residues, a proline (Pro) or gylcine (Gly) in the hydrophobic core region, a serine (Ser) or threonine (Thr) amino acid near the carboxyl terminal end of the hydrophobic core, and an alanine (Ala) or glycine (Gly) at the cleavage site. A mature TSST-1 protein has a coding sequence of 585 base pairs. The entire nucleotide sequence was determined by Blomster-Hautamaazg, et al., as well as by other researchers with other experiments. Consisting of a single polypeptide chain, the structure of holotoxin TSST-1 is three-dimensional and consists of an alpha (α) and beta (β) domain. This three-dimensional structure of the TSST-1 protein was determined by purifying the crystals of the protein. The two domains are adjacent from each other and possess unique qualities. Domain A, the larger of the two domains, contains residues 1-17 and 90-194 in TSST-1 and consists of a long alpha (α) helix with residues 125-140 surrounded by a 5-strand beta (β) sheet. Domain B is unique because it contains residues 18-89 in TSST-1 and consists of a (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 cross mucous surfaces of epithelial cells. Even though TSST-1 consists of several hydrophobic amino acids, this protein is highly soluble in water. TSST-1 is resistant to heat and proteolysis. It has been shown that TSST-1 can be boiled for more than an hour without any presence of denaturation or direct effect on its function.
Read more about this topic: Toxic Shock Syndrome Toxin
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