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YidC : MDFF vs crystal

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made with VMD

Synthesis and placement of new proteins in a living cell poses a challenge for the cellular machinery, in particular in case of so-called membrane proteins. Starting with nothing more than a sequence of DNA, the cell has to translate the genetic code, stitch together the constituent amino acids, and then place the newly made protein where its function is needed, namely the cell membrane. To meet the challenge the cell employs a molecular machine for the synthesis of proteins, the ribosome (see the Dec. 2009 highlight on Managing the Protein Assembly Line ), as well as special proteins that translocate newly synthesized proteins out of the machine into the cell membrane (see the Feb. 2011 highlight on Placing New Proteins ). Depending on the complexity of the membrane protein insertion, different protein systems are used for the translocation, in most cases the systems involving complexes of several, even many, proteins. Now however, the structure and function of the simplest translocating protein system has been solved, which actually is made of only a single protein, called YidC. Despite its simplicity, structure determination of YidC was difficult, taking three decades. Successful structure determination was recently reported here, and involved the combination of cryo-electron microscopy, mutational experiments and computer simulations, the latter using NAMD, VMD and MDFF. The structure that was discovered shows a distinctive arrangement of five trans-membrane helices and reveals how a single copy of YidC interacts with the ribosome at the ribosomal tunnel exit and identifies a site for membrane protein insertion at the YidC protein-membrane lipid interface. The quality of this atomic model is validated by its close agreement with a recently published crystal structure of E. Coli YidC (here). More on our protein translocation website.