pMMO Structure Home Page

Picture
There are two known crystal structures known for pMMO.  They are isolated from two different methanotrophs giving two similar but distinct proteins.  The general structure of the protein (seen in the image to the left) is a series of transmembrane helices and an extra cellular domain which contains the catalytic site.  In both enzymes the active site is a dicopper site coordinated by three histidine residues.  

Protein Orientation in the Membrane

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The protein is oriented as shown in the plasma membrane of the organism.  In this image, the top is the extracellular domain of the protein.  The yellow, green, and purple make up the extra cellular domains containing the catalytic sites outside the membrane.  The rest of the protein is embedded in the membrane, making pMMO an integral membrane protein.  The transmembrane helices are denoted by the magenta, yellow, gray, pink and blue areas.  The protein is embedded in the membrane by the hydrophobic affect.  The transmembrane helices are primary composed of hydrophobic residues.  The extra cellular domain contains both hydrophilic residues on the outer surface of the protein and hydrophobic residues on the inner core of the protein. 

Extracellular Pore

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This image shows the pore in the soluble region outside the cell.  The pore is approximately eleven angstroms in size.  Methane enters the protein through this pore.  It is converted to methanol in the catalytic site before traveling through the pore created by the transmembrane helices into the cell where the methanol is converted to other target molecules.  Methane entering the cell and being converted into methanol is the first step in methanol metabolism which is the main metabolic pathway for methanotropic organisms.  For more information on metabolism see: /biochemistry.html.

Intracellular Pore

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This image shows the pore through the pMMO protein from inside the cell.  The transmembrane helices widen the pore from 11 angstroms in the soluble regions to approximately 22 angstroms which can be seen in this image.  This domain of the protein is made primarily of hydrophobic residues.  The newly converted methanol travels through this pore to enter the cell.

Citations

All images were obtained from the pdb file and manipulated in pymol
PDB file for 1YEW: http://www.pdb.org/pdb/explore/explore.do?structureId=1YEW
Leiberman, R. L., Rosenzweig, A. C., Nature (2005) 434, 177-182
Hakemian, A. S., Kondapalli, K.C., Tesler, J., Hoffman, B. M., Stemmler, B.M., Rosenzweig, A.M., Biochemistry (2008) 47, 6793-6801