Placing New Proteins

Constructing and correctly placing new proteins is a complicated task for living cells. 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. To accomplish these feats, the cell using tools such as the ribosome, a protein factory (see the Dec. 2009 highlight Managing the Protein Assembly Line), and the protein-conducting channel, a switching station within the membrane (see the Nov. 2008 highlight Patching a Leaky Channel). All instructions for making a nascent protein and localizing it, e.g., to the watery cytoplasm or the oily membrane, are carried within its DNA sequence, but how it is read and then executed has long been unclear. Now, two recent research advances picture these processes in astonishing detail. The first advance (reported here), from a collaboration between cryo-electron microscopists and computational biologists using MDFF, shows an atomic level structure that caught the ribosome in the act of inserting a protein into a membrane. The structure reveals the newly forming protein transiting from within the ribosome to the channel and then through an open gate in the protein-conducting channel into the membrane. The second advance (reported here), accomplished with the simulation program NAMD, explained how the ribosome and the protein-conducting channel manage to pay the energy price of insuring a new protein, one amino acid a time, into the membrane. For more information see our protein translocation website.