Despite the variety of protein sizes, shapes, and backbone configurations
found in nature, the design of novel protein folds remains an open problem.
Within simple lattice models it has been shown that all structures are not
equally suitable for design. Rather, certain structures are distinguished by
unusually high designability: the number of amino-acid sequences for which they
represent the unique ground state; sequences associated with such structures
possess both robustness to mutation and thermodynamic stability. Here we report
that highly designable backbone conformations also emerge in a realistic
off-lattice model. The highly designable conformations of a chain of 23 amino
acids are identified, and found to be remarkably insensitive to model
parameters. While some of these conformations correspond closely to known
natural protein folds, such as the zinc finger and the helix-turn-helix motifs,
others do not resemble known folds and may be candidates for novel fold design.Comment: 7 figure