RESUMO
The major protein fraction of the protamine-like PL-II* (phi 2B) from the sperm of Mytilus californianus has been sequenced and characterized. Immunological and sequence analyses unequivocally show that this protein is indeed a member of the histone H1 family. Along with proteins of the histone H1 class, the protein also shows cross-reactivity and sequence identity, in its NH2-terminal region, with the major protamine-like protein component of Mytilus sperm: PL-III (phi 1), of smaller molecular mass. Indeed it is the unusual repetitive sequence motif of the NH2-terminal domain of PL-II* that bestows to this protein its protamine-like nature. Fourier-transform infrared spectroscopy spectroscopy indicates that the protein contains considerable secondary structure: 18% alpha-helix, 21% beta-sheet, 39% turns and bends, 22% random coil. At the higher levels of structure, PL-II* exhibits ionic strength-dependent folding which is indistinguishable from that of histone H5, as monitored by fluorescence anisotropy.
Assuntos
Histonas/química , Proteínas Nucleares/química , Estrutura Secundária de Proteína , Espermatozoides/química , Sequência de Aminoácidos , Animais , Bivalves , Cromatina/química , Cromatografia em Gel , Cromatografia por Troca Iônica , Reações Cruzadas , Proteínas de Ligação a DNA , Endopeptidases , Ensaio de Imunoadsorção Enzimática , Epitopos/análise , Epitopos/química , Polarização de Fluorescência , Análise de Fourier , Histonas/imunologia , Histonas/isolamento & purificação , Immunoblotting , Masculino , Espectrometria de Massas , Dados de Sequência Molecular , Peso Molecular , Proteínas Nucleares/isolamento & purificação , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/isolamento & purificação , Espectrofotometria InfravermelhoRESUMO
We have analyzed the structure of the trypsin-resistant core of the protein PL-II* of the sperm from Mytilus californianus. The peptide has a molecular mass of 8436 Da and its primary sequence is ATGGAKKP STLSMIVAAIQAMKNRKGSSVQAIRKYILANNKG INTSRLGSAMKLAFAKGLKSGVLVRPKTSAGA SGATGSFRVG. This sequence bears an enormous homology and fulfills the constraints of the consensus sequence of the trypsin-resistant peptides of the proteins of the histone H1 family. Secondary structure analysis using Fourier-transform infared spectroscopy as well as predictive methods indicate the presence of 20-30% beta-structure and approximately 25% alpha-helix for this peptide. As in the case of histone H1 proteins, the protein PL-II* core exhibits a compact globular structure as deduced from hydrodynamic measurements. The presence of a histone H1 protein with protamine-like features, seems to be thus, a common general feature of the chromatin composition in the sperm of the bivalve molluscs.
