Sandbox Reserved 325: Difference between revisions

The gene Rv1885c from ''Mycobacteria tuberculosis'' encodes for a non-functional chorismate mutase (*MtCM)<ref name="pizza" />. This non-functional mutase has a 33-amino-acid cleavable sequence <ref name="pizza" />. Chorismate mutase is a vital enzyme in the shikimate pathway, which allows for the synthesis of tryptophan, tyrosine, and phenylalanine <ref name="pizza" />. This protein acts at the first branch point of the shikimate pathway, making it a regulating step in the conversion of prephenate from chorismate<ref name="CMW2"> PMID:11481470 </ref>. Since chorismate mutase catalyzes a claisen rearrangement it can be considered an isomerase since it catalyzes rearrangements of isomers.  Chorismate mutase provides a 2x10⁶ fold increase in the rate of reaction in comparision to the uncatalyzed reaction <ref > P.D. Lyne, A.J. Mulholland, W.G. Richards. Insights into chorismate mutase catalysis from a combined qm/mm simulation of the enzyme reaction. Journal of the American Chemistry Society. 1995 117(45):11345-11350</ref>.

Chorismate mutase only occurs in bacteria, higher plants, and fungi, due to the fact that the shikimate pathway is only found in these organisms <ref name="strat" />. In ''Escherichia coli'', chorismate mutase has a periplasmic destination<ref name="pizza" />. In ''M. tuberculosis'' there is in abscence of a periplasmic compartment for chorismate mutase, so it secretes into the culture filtrate of ''M. tuberculosis''<ref name="pizza" />. It is believed that a pseudoperiplasmic space might exist in ''M. tuberculosis''<ref name="pizza" />.

The N-terminal sequence of ''M. tuberculosis'' chorismate mutase is able to  function in ''E. coli'' which suggests that ''M. tuberulosis'' chorismate mutase belongs to the AroQ class of the chorismate mutases<ref name="CMArt2"> PMID:15737998 </ref>.

Rv1885c is synthesized along with the 33-amino-acid terminal sequence, which when expressed with ''E. coli'', is cleaved off the mature protein<ref name="pizza"  />. Chorismate mutase is the only example of an enzyme catalyzing a percyclic reaction <ref name="strat"> PMID:10960481 </ref>.

Chorismate mutase is a homodimer which has an predominantly α-helical structure <ref name="pizza" />. There are 10 α-helices spread across the two monomers of chorismate mutase <ref name="pizza" />. Approximately 86% of the amino acid residues are in the α-helical formations <ref name="pizza" />. The α-helical structure of ''M. tuberculosis'' chorismate mustase similar to the chorismate mutases of ''S. cerevisae'' and ''E. coli'' <ref name="pizza" />. It holds its dimeric state in a protein concentration as low as 5 nM <ref name="pizza" />. There are no β-sheets present in chorismate mutase <ref name="CMArt2" />  

Chorismate has an active site, which is used for the catalysis of the shikimate pathway <ref name="pizza" />. The <scene name='Sandbox_Reserved_325/Active_site/1'>active site</scene> is made of Arg ₄₉,Lys ₆₀, Arg ₇₂, Thr ₁₀₅, Glu ₁₀₉, and Arg ₁₃₄<ref name="pizza" />. This active site exists through electrostatic interactions with chorismate and hydrogen bonding between the amino acids <ref name="CMArt2" />.  The active site forms within a single chain <ref name="pizza" />. The active site can form without any help from the second half of the dimer <ref name="pizza" />.

The molecular weight of chorismate mutase is 36,000 Da <ref name="pizza" />. Based on the fact that each monomeric subunit has a molecular weight of 18,474 Da, the molecular weight of the molecule supports the theory that it is a dimer <ref name="pizza" />. This is also supported by the fact that all chorismate mutases that occur naturally are either trimers or dimers <ref name="pizza" />. ''M. tuberculosis'' chorismate mutase is similar to the chorismate mutases of yeast and ''E. coli'' in the regards that they all are homodimers <ref name="CMArt2" />

There are no allosteric regulatory sites on chorismate mutase, which supports the theory that it is not regulated by the aromatic amino acids that are the products of the shikimate pathway <ref name="pizza" />.

There is one <scene name='Sandbox_Reserved_325/Disulfide/1'>disulfide bridge</scene> in chorismate mutase <ref name="pizza" />. It is between Cys ₁₆₀ and Cys ₁₉₃ <ref name="pizza" />.

Chorismate mutase has a 33-amino-acid cleavable sequence <ref name="pizza" />. The N-terminal sequence of ''M. tuberculosis'' chorismate mutase is able to  function in ''E. coli'' which suggests that ''M. tuberulosis'' chorismate mutase belongs to the AroQ class of the chorismate mutases<ref name="CMArt2" />. Another factor that suggests that ''M. tuberculosis'' chorismate mutase belongs to the AroQ class of chorismate mutases is that it has has a predominantly α-helical structure, which is similar to the chorismate mutases of ''E. coli'' and yeast, which also belong to the AroQ group of chorismate mutases <ref name="CMArt2" />.

in Michaelis-Menten kinetics it has Km of 0.5 ± 0.05 mM and Kcat of 60 s^-1 <ref name="pizza" />.

Chorismate mutase is an essential enzyme in the shikimate pathway <ref name="pizza"> PMID:17146044 </ref>. This pathway allows for the biosynthesis of aromatic amino acids tryptophan, tyrosine, and phenylalanine <ref name="pizza" />. The production of tyrosine and phenylalanine is achieved by what is called a Claisen rearrangement. first converting chorismate to prephenate.  Prephenate then reacts with prephenate dehydratase and prephenate dehydrogenase which forms phenylpyruvate and hydroxyphenylpyruvate.  After this occurs, aminotransferase converts hydroxy-phenylpyruvate and phenylpyruvate to phenylalanine and tyrosine.  Chorismate mutase provides a 2x10⁶ fold increase in the rate of reaction, in comparison to the uncatalyzed reaction <ref > P.D. Lyne, A.J. Mulholland, W.G. Richards. Insights into chorismate mutase catalysis from a combined qm/mm simulation of the enzyme reaction. Journal of the American Chemistry Society. 1995 117(45):11345-11350</ref>. It is the only example of an enzyme catalyzing a percyclic reaction <ref name="strat"> PMID:10960481 </ref>

Tuberculosis has developed various mechanisms to survive in hostile environments <ref name="CMArt2" />. The emergence of multi-drug resistant tuberculosis and other diseases such as AIDS compound the problem of how to treat tuberculosis <ref name="CMArt2" />. Chorismate mutase may be involved in pathogenesis <ref name="pizza" />. Researchers are currently looking into new antimicrobial drugs for diseases such as tuberculosis <ref name="pizza" />. These new drugs would take advantage of the fact that chorismate mutase and the shikimate pathway do not occur in humans, to target and treat various forms of tuberculosis <ref name="pizza" />. ''M. tuberculosis'' chorismate mustase is believed to have a role in the survival of ''M. tuberculosis'' <ref name="CMArt2" />. Two genes in ''M. tuberculosis'', Rv0948c and Rv1885c code for chorismate mutase <ref name="CMArt2" />. These help support ''M. tuberculosis'' when aromatic amino acids, such as tryptophan, tyrosine, and phenylalanine, are deficient <ref name="CMArt2" />. Some researchers have proposed that a proline-rich section of ''M. tuberculosis'' chorismate mutase might be responsible for it binding to the surface receptors on the host cell marcophages <ref name="CMW1"> PMID: 16752890 </ref>.