Function
is found in Vibrio cholera. Its function is cleaving A subunit of cholera toxin, which may contribute to intestinal growth or pathogenesis. The substrate of VesB is any protein containing arginine (XXRXX) where R is arginine and X is other amino acids, and the products after cleavage are (XXR+XX).
Disease
Cholera is a bacterial disease of the small intestine that is spread through contaminated food or water. Its symptoms include severe diarrhea and dehydration. Impoverished areas with lesser sanitation are most susceptible to cholera. It is potentially fatal if left untreated.
Relevance
By studying VesB, improved treatment and prevention of cholera could be discovered. While it is not a major problem in the United States, lives could be improved and saved in areas such such as Africa, where cholera is more prevalent. This would allow more social interaction without concern of disease, which would be beneficial as many people are in close contact in these areas of contamination.
Structural Highlights
The main of VesB is beta sheets, with some alpha helices and a few random coils. VesB has two and that make up its tertiary structure. There is an N-terminal (Green) protease domain with a trypsin/chymotrypsin fold and also a C-terminal (Red) Ig fold. These different domains result in different stability and folds, as well as their ability to evolve and function. shows the shape and dimensions of the molecule, as well as the shapes of surface a conformer might present. There are both sections of VesB. Pink is polar, gray is hydrophobic, and red is oxygen. Its surface is closely split between hydrophilic and hydrophobic. The alpha helices make up the majority of the hydrophilic areas, showing areas where water would be attracted to VesB. The crystal structure of VesB was solved without a ligand, however, any protein containing RX (R is arginine, X is another amino acid) is a VesB ligand. His78, Asp125, and Ser221 make up the VesB . Aspartic acid is deprotonated and proton transfer moves from histidine to aspartic acid, meaning histidine is also deprotonated. Histidine then accepts a proton from serine's hydroxyl group, allowing serine to attack a substrate. This trio of amino acids work together to help VesB effectively cleave the substrate. Asp194 (Red) and Asp 220 (Black) coordinate the N terminus amino group in active VesB. Ile16 (Green) and Ile33 (Blue) occupies the hydrophobic pocket while Val159 (Yellow) and Val180 (Orange) assist in hydrogen bonding. These amino acids help form the of VesB. Leu158 (Brown) assists in cleaving the substrate. Tyr 250 (Purple) coordinates an Na+ ion that binds to and allosterically enhances thrombin activity. Proline residue near Lys224 (Pink) inhibits this Na+ ion binding.
Kinetic Data
VesB is uncompetitively inhibited by Boc-Gln-Ala-Arg-7-amino-4-AMC. This shows that this peptide does not have an impact on VesB function and that VesB is able to effectively cleave substrate.
