Structure and function of protamines: An investigation of clupeine properties by nuclear magnetic resonance

Abstract

AbstractIn this paper a detailed study of the structural properties of the three main fractions YI, YII, and Z of clupeine (protamines) has been performed with the aid of nuclear magnetic resonance methods. The investigation includes chemical shift data of protons and C‐13 nuclei and measurement of the T1 relaxation times of the C‐13 nuclei. These data demonstrate that the flexibility of the three fractions is different and that in the presence of inorganic phosphate fraction YI exhibits structural changes more relevant than the other two fractions. The measurement of the relaxation times, under the assumption of a rigid ellipsoid model, gives an estimate of the rough molecular size of the clupeine fractions. Different side chain mobilities that complement the previous observations based on chemical shift data are determined. A further extension of this work concerns the interaction of the clupeines with natural mononucleotides. An appreciable interaction takes place between fraction YI and purinic nucleotides while a simple electrostatic interaction seems to exist with the other two fractions. A possible explanation of this different behavior seems to involve the formation of large aggregates solely in the case of fraction YI.