Prediction of fragile points of coiled coils

A prediction system for identifying the region of flexible regions of the coiled coil was developed to determine the bending positions of the myosin rods using atomic force microscopy (AFM) and to analyze the molecular structures of proteins containing coiled coils. The prediction system comprises two modules: identification of heptad break points and prediction of fragile points in the coiled coil due to the hydrophilic core or hydrophobic outfield region. Here, we investigated the myosin rods using this prediction system. The results of AFM imaging showed four main flexible regions in a single myosin rod and of the 17 possible fragile points predicted, 16 were located in the four experimental bending regions. Next, we examined the enhanced fluctuation around these predicted fragile points using the B-factor for the three dimensional structure of coiled coil proteins from the SCOP database and found that the fluctuations in the hydrophilic core regions were significantly larger than those in the regions of the normal coiled coil. In contrast, the fluctuations in the hydrophobic outfield regions were reduced, suggesting a structural change of the coiled coils to balance these regions. Thus, the dynamic changes in the structure of the coiled coils around the fragile points may be related to the biological functions of the proteins. The prediction tool which developed in this work was incorporated in the SOSUIcoil system which predicts the coiled coil regions.