Fluorescence studies on clupein protamines: Evidence for globular conformation

Are there molecules of nucleoprotamine?

“…It follows that it is not the considerations concerning the secondary structure of protamine but rather the turns of the chain due to the presence of proline and glycine residues, and intramolecular interactions that shape the the tertiary structure of the molecule. (14,17,58) In contrast to the earlier view, it could be imagined that the conformation of oligoarginine stretches is relatively free and could be adjusted when bound to DNA. In short, it can be supposed that nonbasic amino acids determine the internal structure of the protamine molecule, whereas basic residues are responsible for the interaction with DNA.…”

“…(47) Additional support for the globular nature of the protamine molecule is provided by the experimental evidence for the proximity of N-and C-terminal residues. (17,48) Dark field electron microgrphs indicate that the unstained, unshadowed molecules are ellipsoidal in shape: about 25 Å in the shorter dimension, and 35-40 Å in the longer. (36) However, it is uncertain whether it is justified to consider the complex formation in vivo to take place between an unmodified protamine and DNA, which leads to question the whole strength of evidence obtained regarding complexes in vitro.…”

“…However, they acquire somewhat more compact conformation in solution upon addition of 0.5 M phosphate, (43) 0.1 M TRIS, (17) 0.3 M NaCl, (44) or millimolar amounts of nucleotides. (45) Fractions YI and Z of clupeine exhibit reduced mobility in some sections of their molecules in the presence of a large excess of phosphate ions.…”

“…Since the protamine is a small molecule as compared with other proteins, the fraction of amino acids involved in turns or otherwise untypical conformations is expected to be quite significant. (17,37,38) When protamine molecules are regarded as globular entities, the tertiary structure of the molecule could be stabilized by interactions between hydrophobic amino acids as well as possible H-bonds provided by serine and threonine residues. It follows that it is not the considerations concerning the secondary structure of protamine but rather the turns of the chain due to the presence of proline and glycine residues, and intramolecular interactions that shape the the tertiary structure of the molecule.…”

“…Unfortunately, it has been impossible to track the C ␣ spine of the protamine molecule in the X-ray structure of Zn-insuline co-crystallized with protamine. (41) It has also been supposed that protamine molecules free in solution could attain some other conformation; for instance, polyproline II helix (42) or ␤-structure, (17) whereas when complexed with DNA, 1=3 hydrogen bonding (␥-ribbon) has been suggested. (20) Due to the lack of crucial evidence concerning the secondary structure of regions bound to DNA, these regions are referred to below as ''structured.…”