Refinement of the Model Structure

Abstract

From isomorphous replacement or molecular replacement an approximate model of the protein structure can be obtained in which the broad features of the molecular architecture are apparent. Structure factors calculated on the basis of this model are generally in rather poor agreement with the observed structure factors. The agreement index between calculated and observed structure factors is usually represented by an R-factor as defined in Eq. (13.1). Thus an R-factor of 50% is not uncommon for the starting model, whereas for a random acentric structure it would be 59% (Wilson, 1950).