ELECTROSTATIC GRADIENTS IN IRON STORAGE PROTEIN FERRITIN

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The electrostatically driven Monte Carlo (EDMC) method has been greatly improved by adding a series of new features. A procedure for cluster analysis of the accepted conformations was included. This information is used in the proedure to guide the search for the global minimum. Also, alternative procedures for generating perturbed conformations - used for sampling the conformational space - were included. These procedures are found to enhance the efficacy of the method by generating a larger number of low-energy conformations. The improved EDMC method has been used to explore the conformational space of a 20-residue polypeptide chain whose sequence corresponds to the membrane-bound portion of melittin. The ECEPP/3 algorithm was used to describe the conformational energy of the chain. After an exhausting search involving 14 independent runs of the procedure, the lowest-energy conformation (LE) (-91.0 kcal/mol) of the entire study was encounagered in four of the runs, while conformations higher in energy by no more than 1.8 kcal/mol were found in the remaining runs with the exception of run 8. LEC is identical to the conformation reported recently by Lee, et.al. (1997) as the lowest-energy conformation obtained in their study using the conformational space annealing method. These results suggest that this conformation may correspond to the global energy minimum of the ECEPP/3 potential function for this specific sequence.