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Protamines: Structural Complexity, Evolution and Chromatin Patterning

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Abstract:

Despite their relatively arginine-rich composition, protamines exhibit a high degree of structural variation. Indeed, the primary structure of these histone H1-related sperm nuclear basic proteins (SNBPs) is not random and is the depository of important phylogenetic information. This appears to be the result of their fast rate of evolution driven by positive selection. The way by which the protein variability participates in the transitions that lead to the final highly condensed chromatin organization of spermatozoa at the end of spermiogenesis is not clearly understood. In this paper we focus on the transient chromatin/nucleoplasm patterning that occurs in either a lamellar step or an inversion step during early and mid-spermiogenesis. This takes place in a small subset of protamines in internally fertilizing species of vertebrates, invertebrates and plants. It involves “complex” protamines that are processed, replaced, or undergo side chain modification (such as phosphorylation or disulfide bond formation) during the histone-to-protamine transition. Characteristic features of such patterning, as observed in TEM photomicrographs, include: constancy of the dominant pattern repeat distance λm despite dynamic changes in developmental morphology, bicontinuity of chromatin and nucleoplasm, and chromatin orientation either perpendicular or parallel to the nuclear envelope. This supports the hypothesis that liquid - liquid phase separation by the mechanism of spinodal decomposition may be occurring during spermiogenesis in these species. Spinodal decomposition involves long wave fluctuations of the local concentration with a low energy barrier and thus differs from the mechanism of nucleation and growth that is known to occur during spermiogenesis in internally fertilizing mammals.





Keywords: ARGININE-RICH PROTAMINES; HISTONE H1; LAMELLAR; Patch; Protamines; SPERMATIDS; Spinodal decomposition; chromatin/nucleoplasm patterning; evolution; genome; keratinous protamines; lamellae; nucleation; phylogeny; protamine SNBP type; sperm nuclear basic proteins; spermiogenesis; spinodal decomposition; structural heterogeneity; structure; thermal quenching

Document Type: Research Article

DOI: http://dx.doi.org/10.2174/092986611795713989

Publication date: August 1, 2011

More about this publication?
  • Protein & Peptide Letters publishes short papers in all important aspects of protein and peptide research, including structural studies, recombinant expression, function, synthesis, enzymology, immunology, molecular modeling, drug design etc. Manuscripts must have a significant element of novelty, timeliness and urgency that merit rapid publication. Reports of crystallisation, and preliminary structure determinations of biologically important proteins are acceptable. Purely theoretical papers are also acceptable provided they provide new insight into the principles of protein/peptide structure and function.
ben/ppl/2011/00000018/00000008/art00002
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