3.1 Papers
3.1.6 Chronological list
3.1.6.37 Cardozo, T., Totrov, M., and Abagyan, R. (1995). Homology modeling by the ICM method. Proteins: Structure, Function, Genetics, 23, 403-414
Five models have been built by the ICM method for the Comparative Modeling section of the Meeting on the Critical
Assessment of Techniques for Protein Structure Prediction. The targets have homologous proteins with known
three-dimensional structure with sequence identity ranging from 25 to 77%. After alignment of the target sequence with the
related three-dimensional structure, the modeling procedure consists of two subproblems: side-chain prediction and loop
prediction. The ICM method approaches these problems with the following steps: (1) a starting model is created based on
the homologous structure with the conserved portion fixed and the nonconserved portion having standard covalent
geometry and free torsion angles; (2) the Biased Probability Monte Carlo (BPMC) procedure is applied to search the
subspaces of either all the nonconservative side-chain torsion angles or torsion angles in a loop backbone and surrounding
side chains. A special algorithm was designed to generate low-energy loop deformations. The BPMC procedure globally
optimizes the energy function consisting of ECEPP/3 and solvation energy terms. Comparison of the predictions with the
NMR or crystallographic solutions reveals a high proportion of correctly predicted side chains. The loops were not correctly
predicted because imprinted distortions of the backbone increased the energy of the near-native conformation and thus
made the solution unrecognizable. Interestingly, the energy terms were found to be reliable and the sampling of
conformational space sufficient. The implications of this finding for the strategies of future comparative modeling are
discussed.