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A highly accurate and novel method for reconstructing protein backbones from alpha carbon traces is described by Benjamin Moore, Lawrence Kelley, James Barber, James Murray, and James MacDonald on page 1881. Gaussian mixture models are used to build a “structural alphabet”, in this case a library of short alpha carbon fragments aligned on a central peptide bond. These are then fitted to alpha carbon protein models to estimate the positions of the missing backbone atoms. The cover image depicts several of the “letters” that make up the alphabet, surrounding an alpha carbon trace and reconstructed protein model. The method is available as a C++ source code and a webserver implementation at