Biochemistry I   Spring & Fall Terms

Maltoporin Structure

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  Membrane thickness.
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  "Helical Slide" Residues

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Maltoporin from Salmonella typhimurium
The porins are outer membrane proteins that facilitate the diffusion of small molecules into the periplasmic space of bacteria. Maltoporin* from Salmonella typhimurium is shown with bound maltotrioside. The initial view of the trimer is from the extracellular side. Each subunit is an 18-stranded, antiparallel, b-barrel. The extracellular surface is characterized by large loops, colored separately above. The nitrophenyl-maltotrioside bound to each subunit is shown spacefill, colored CPK; a Ca2+ ion at the center of the trimer is spacefill (Fig. 2a).
The "helical slide" of aromatic residues inside one of the subunits are shown as white sticks. Several of these are involved in the binding of the transported sugars. The nitrophenyl-maltotrioside is Ball & Stick, colored green (Fig. 2b).

Viewing Tip:
Use the Chime menu choices as follows: select the aromatic residues; then spacefill Display; and finally color purple (or whatever you want). Note that the aromatics form two "belts" on the outside of the b-barrels; these strips correspond to the interfaces of the membrane-aqueous boundaries. This feature is similar to that seen in the structure of the K+-Channel and other integral membrane proteins.

*The structure of the maltoporin from Salmonella typhimurium is described by Meyer et al. (1997) J. Mol. Biol. 266 761-775. The coordinate file is 2MPR.pdb. (References to Figs. above are to those of Meyer et al.)

Four more membrane protein structures:
 Bacteriorhodopsin       K+-Channel       Maltoporin       a-Hemolysin       Reaction Center

Back to the Protein Structure List.

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8.21.04