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Methenyl-tetrahydromethanopterin Cyclohydrolase and Methylene

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					Methenyl-tetrahydromethanopterin
Cyclohydrolase and Methylene-
tetrahydromethanopterin Reductase

              Lindsey Wargo
              22 March 2007
       Advanced Biophysical Chemistry
                       Methanogens
   Methanogens
       Can produce methane from substrates including:
           Carbon dioxide and molecular hydrogen
           Acetate
           Methylthiols and methylamines
   Carbon Dioxide and Molecular Hydrogen
    Pathway to Methane
       Involves 10 methanogen specific enzymes
           Methenyltetrahydromethanopterin cyclohydrolase
           Methylenetetrahydromethanpterin reductase
Structure of H4MPT compared to H4F




                     Taken from Shima, Warkentin, Thauer, and
                     Ermler (2002); Journal of Bioscience and
                     Bioengineering, 93: 519-530
Methanogenic Pathway Utilizing Carbon
  Dioxide and Molecular Hydrogen




Taken from Shima, Warkentin, Thauer, and Ermler (2002); Journal of Bioscience and Bioengineering, 93: 519-530
            Methenyltetrahydromethanopterin
                 cyclohydrolase (Mch)
                                                           Catalyzes conversion of
                                                            formyl-H4MPT to
                                                            methenyl-H4MPT
                                                           Next step uses enzyme
                                                            methylene-H4MPT
                                                            dehydrogenase
                                                            (coenzyme F420 can
                                                            serve as a hydride
                                                            donor)
Taken from Shima, Warkentin, Thauer, and Ermler
(2002); Journal of Bioscience and Bioengineering, 93:
519-530
          Methylenetetrahydromethanpterin
                  reductase (Mer)
                                                       Reduces methylene-
                                                        H4MPT to methyl-
                                                        H4MPT at expense of
                                                        F420H2




Taken from Shima, Warkentin, Thauer, and Ermler
(2002); Journal of Bioscience and Bioengineering,
93: 519-530
             Methenyltetrahydromethanopterin
                  cyclohydrolase (Mch)
                                                                 1 type of subunit
                                                                 No prosthetic group
                                                                 Stable in air
                                                                 Homotrimeric enzyme
                                                                 Unique α/β fold
                                                                  composed of 2 domains
                                                                  forming a large pocket
                                                                  between them
               Crystal Structure Obtained from:
http://www.rcsb.org/pdb/explore/explore.do?structureId=1QLM
           Methenyltetrahydromethanopterin
                    cyclohydrolase
                                                           Arrow indicates position
                                                            of substrate pocket
                                                           Pocket Size
                                                           Presence of aromatic
                                                            side chains on one side
                                                            of the pocket
                                                           2 clusters of positively
                                                            charged amino acids

Taken from Shima, Warkentin, Thauer, and Ermler
(2002); Journal of Bioscience and Bioengineering, 93:
519-530
              Methylenetetrahydromethanpterin
                         reductase
                                                                 1 subunit
                                                                 No prosthetic groups
                                                                 Stable in air
                                                                 Ternary complex
                                                                  catalytic mechanism
                                                                 Monomer composed of
                                                                  (βα)8 barrel (TIM
                                                                  barrel) fold
                                                                 Differs from typical
              Crystal Structure Obtained from:
http://www.rcsb.org/pdb/explore/explore.do?structureId=1Z69
                                                                  barrel fold
          Methylenetetrahydromethanpterin
                     reductase
                                                       Cleft formed (proposed
                                                        substrate binding site)
                                                        by interaction of
                                                        insertion regions & C-
                                                        terminal end of barrel
                                                       Unusual cis-peptide
                                                        bond (bulge at end of
                                                        strand β3)
                                                           Involved in binding
Taken from Shima, Warkentin, Thauer, and Ermler             deazaflavin ring
(2002); Journal of Bioscience and Bioengineering,
93: 519-530
                  Conclusions

   Both the functions and the crystal structures
    have been determined for the enzymes
    involved in the methanogenic pathway using
    carbon dioxide and molecular hydrogen
    specifically
    methenyltetrahydromethanopterin
    cyclohydrolase (Mch) and
    methylenetetrahydromethanpterin
    reductase (Mer).

				
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