Biophysical study of a molecular intermediate preceding collapse of tight couple and Kaltschmidt–Wittmann ribosomes

Abstract

In previous works we evidenced, by di¡erent biophysical approaches, two levels of structural organization in Escherichia coli ribosomal particles. Thermal treatment up to a de¢ned and non-denaturing temperature causes demolition of only one level of structural complexity. By consequence the ribosomal particle exists in an intermediate state between the native form and the completely collapsed one. In this communication we report on a structural comparison of this intermediate state in Kaltschmidt^Wittmann (LC) and 'tight couple' (TC) ribosomes. Three di¡erent biophysical approaches were adopted : dielectric spectroscopy, £uorescence and light scattering. Di¡er-ential responses to thermal treatment are evidenced in the two ribosomal species. In particular TC show a more compact structure and the overall particle population is more homogeneous than LC in the native state. On the other hand, LC particles after thermal treatment undergo major alterations of geometry and/or phenomena of supra-particle aggregation. ß