Secondary structure prediction of protamines

Abstract

Protamines are rery basic, small proteins with about 70% arginine content. Molecular weight ranges from 4000 in fish to ∼6000–7000 in mammals and birds. During spermatogenesis protamines replace histones to build an extremely compact DNA protamine complex in which transcription is inhibited. Circular dichroism. X-ray diffraction and electron microscopy studies have yielded different and non compatible models for the mechanism of interaction between DNA and protamine. Chou and Fasman's method for prediction of secondary structure based on primary structure data allows us to postulate a unique structural pattern for protamines obtained from fish, mammals and birds. The main feature of the structure is the presence of β-turns which give rise to parallel chains with or without β-sheet configuration. The β-turns give a strong globular character to the molecular, the presence of α-helix being excluded from the structure. This structural model permits us to reconcile some of the existing models with the experimental data available.