Quantitative fitting of atomic models into observed densities derived by electron microscopy

A new methodology for fitting atomic models into density distributions is d escribed. This approach is based on a global density correlation analysis t hat can be optionally supplemented by biochemical as well as biophysical da ta. The procedure is completely general and enables an objective evaluation of the resulting docking in the light of available biochemical and biophys ical information as well as density correlation alone. In this paper we des cribe the implementation of the algorithm and its application to two biolog ical systems. In both cases the procedure provided an interface model on th e atomic level and located parts of the structure that were missing in the atomic model but present in the electron-microscopic construct. It also det ected and quantified conformational changes in actomyosin complexes. (C) 19 99 Academic Press.