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=Chorismate Mutase=
=Chorismate Mutase=
==Introduction==
==Introduction==
The gene Rv1885c from ''Mycobacteriam 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:PMC55368 </ref>.  Chorismate mutase provides a 2x10<sup>6</sup> fold increase in the rate of reacrion 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>
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 2x10<sup>6</sup> 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>


==Structure==
==Structure==
<Structure load='2f6l' size='300' frame='true' align='left' caption='Insert caption here' scene='Sandbox_Reserved_325/Chainbows/1' />
<Structure load='2f6l' size='300' frame='true' align='left' caption='Chorismate Mutase' scene='Sandbox_Reserved_325/Chainbows/1' />


Chorismate mutase is a homodimer which has an all-α-helical structure <ref name="pizza" />. There are 10 α-helicies spread across the two monomers of chorismate mutase <ref name="pizza" />. Aprozimately 86% of the amino acid residues are in the α-helicial formations <ref name="pizza" />. The α-helical structure of ''M. tuberculosis'' chorismate mustase similar to the chorismate mutases of ''S. cerevisae'' and ''E. coli''.  It holds its dimeric state in a protein concentration as low as 5 nM <ref name="pizza" />. There are no β-sheets in chorismate mutase <ref name="CMArt2" />
Chorismate mutase is a homodimer which has a 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 *MtCM are 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 active site is made of Arg <sub>49</sub>,Lys <sub>60</sub>, Arg <sub>72</sub>, Thr <sub>105</sub>, Glu <sub>109</sub>, and Arg <sub>134</sub><ref name="pizza" />. This active site exists through electrostatic interactions with chorismate and hydrogen bonding between the amino acids <ref name="CMW2" />.  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" />


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 <sub>49</sub>,Lys <sub>60</sub>, Arg <sub>72</sub>, Thr <sub>105</sub>, Glu <sub>109</sub>, and Arg <sub>134</sub>.<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" />


not regulated by aromatic amino acids, which is supported by the fact that there are no allosteric regulatory sites.
The molecular weight of *MtCM is 36,000 Da.<ref name="pizza" />  Based on 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 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" />


quaternary structure determined by molecular sieve chromatography
There are no allosteric regulatory sites on *MtCM, which supports the theory that chorismate mutase is not regulated by the aromatic amino acids that are the products of the shikimate pathway.<ref name="pizza" />
works best at 37 deg C ph 7.5
1 S-S bond between Cys 160 and cys 193
aroQ
ph tolerance from 4.0 to 7.5 for optimal activity
no beta sheets 222222
Mtb Chorismate Mutase Is a Dimeric Protein with a Predominantly
�-Helical Structure—Whereas catalytic activity and
regulatory activity of Mtb chorismate mutase point toward
some novel properties of the enzyme, the study was continued
to determine the biophysical parameters of the enzyme to define
the actual class to which it belongs. Size exclusion chromatography
was performed to determine the oligomeric state of
the protein. The output was a single peak corresponding to the
dimeric state of the recombinant protein (data not shown). In this
context, Mtb chorismate mutase is similar to the E. coli or yeast
chorismate mutases, which are also dimers of identical subunits
(24, 36). To determine the secondary structure of Mtb chorismate
mutase, the CD spectrum was recorded on a JASON spectropolarimeter
(Fig. 6). The data were analyzed using the K2D software
available on-line. The results suggest a predominantly
�-helical structure for the enzyme. This is reminiscent of the
AroQ class of enzymes from yeast and E. coli (24, 37) that are also
helical proteins. Members of the AroQ class of chorismate mutases
consist of unregulated and regulated (AroQr) enzymes and
are unusually divergent among closely related organisms (38).
This structure showed 71% helices with essentially no �-sheets. 2222222222


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


here is a <scene name='Sandbox_Reserved_325/Disulfide/1'>disulfide bridge</scene>
==Mechanism==
==Mechanism==
in michaelis menten kinetics it has Km of 0.5 ± 0.05 mM and Kcat of 60 s<sup>-1 </sup>
in Michaelis-Menten kinetics chorismate mutase has Km of 0.5 ± 0.05 mM and Kcat of 60 s<sup>-1 </sup>.<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 arrangement. 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 2x10<sup>6</sup> 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>


==Chorismate Mutase and Tuberculosis==
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.<ref name="pizza" /> First by converting chorismate to prephenate.<ref name="pizza" />  Prephenate then reacts with prephenate dehydratase and prephenate dehydrogenase which forms phenylpyruvate and hydroxyphenylpyruvate.<ref name="pizza" />  After this occurs, aminotransferase converts hydroxy-phenylpyruvate and phenylpyruvate to phenylalanine and tyrosine.<ref name="pizza" />  Chorismate mutase provides a 2x10<sup>6</sup> 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>
may be involved in pathogenesis.
 
one can take advantage of non-occurance of CMs in humans to try to develop antimicrobial drugs for human pathogens such as tb
Chorismate mutase has optimal performance at 37 degrees Celcius and at pH 7.5, but it can still optimally a pH range from pH 4.0 to 7.5 <ref name="pizza" />
no func in non-shik pathways like those of macrophages of mammals. target this for TB infection
ph is 4.5 om tb macrophage enviro. acidic.


Mycobacterium tuberculosis (Mtb)1 has developed ingenious
mechanisms to survive inside the hostile environment presented
by the host and to acquire essential nutrients from this
adverse environment (1–3). The emergence of drug-resistant
strains and synergy with the AIDS virus has further aggravated
the disease scenario (4–6). For the development of new
therapeutic intervention strategies, there is a need for identification
of novel targets that are not only unique to Mtb but
blocking of which would either prove lethal to the bacterium or
render it extremely susceptible to the host immune response.
In this context, understanding the mechanism of action of the
aromatic amino acid pathway enzymes of Mtb assumes the
utmost importance because most of the corresponding genes
have been proven essential for the bacterium and have no
human or mammalian counterpart (7, 8). Moreover, amino acid
auxotrophs of Mtb do not survive or multiply in macrophages
(9, 10), suggesting that these amino acids are not available
within the compartment of the macrophage in which the bacteria
reside.
displayed by another hypothetical protein coded by
open reading frame Rv0948c, a novel instance of the
existence of two monofunctional chorismate mutase 2222222222222222222222222


==Chorismate Mutase and Tuberculosis==
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" />  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>


==References==
==References==
<references/>
<references/>
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