α-Helix–double helix interaction shown in the structure of a protamine-transfer RNA complex and a nucleoprotamine model

Abstract

Single crystal X-ray diffraction and circular dichroism studies of protamine binding to a tRNA suggest that the protamine molecule changes its conformation from a random coil to a structure containing α helices on binding to tRNA, and that α-helical segment(s) of protamine bind approximately along a shallow groove of a double-helical portion of tRNA. Based on these observations, a structural model for nucleoprotamine is proposed.