ABSTRACT
Introducción: Las histonas H1 modulan la estructura y la función de la cromatina. Las células somáticas de mamífero contienen los subtipos H1º, H1a, H1b, H1c, H1d y H1e; en células germinales de testículo y en ovocito, se encuentran respectivamente H1t y H1oo. Su estructura está conformada por un dominio central globular flanqueado por los dominios N-Terminal (DNT) y C-Terminal (DCT). Objetivo: Caracterizar la estructura secundaria de subtipos de la histona H1 mediante dicroísmo circular (DC). Materiales y Métodos: La histona H1 total se extrajo de núcleos de cerebro de rata por cromatografía de intercambio catiónico; la H1º se purificó por filtración en gel y las H1a, H1b, H1c y H1e por cromatografía líquida de alta resolución de fase reversa (RF-HPLC). Los espectros de DC se realizaron en tampón fosfato 10 mM; tampón fosfato 10 mM, 20% TFE (trifluoroetanol); tampón fosfato 10 mM, 40% TFE; tampón fosfato 10 mM, 60% TFE; tampón fosfato 10 mM, 150 mM NaCl y tampón fosfato 10 mM, 1 M NaCl. El análisis de los espectros se realizó con el programa Standard Analysis. Resultados: El porcentaje de hélice-alfa se calculó por diferentes métodos matemáticos teniendo en cuenta elipticidad molar a 193 nm y a 222 nm; con programa de deconvolución K2D y con relaciones cualitativas R1 y R2. El TFE induce la estructura en hélice-alfa en cada uno de los subtipos, mientras que NaCl no induce ningún cambio importante. Conclusión: Los subtipos con mayor contenido de hélice-alfa son H1a y H1c. Las diferencias observadas en el porcentaje de hélice-alfa entre los diferentes subtipos puede ser importante para su diferenciación funcional.
H1 histones modulate the structure and function of chromatin. Mammalian somatic cells contain H1º, H1a, H1b, H1c, H1d and H1e subtypes; H1t and H1oo are found in testicular germ cells and oocyte, respectively. Its structure consists of a globular core domain flanked by N-terminal (DNT) and C-terminal (DCT) domains. Objective: To characterize the secondary structure of histone H1 subtypes through circular dichroism (CD). Materials and Methods: Total histone H1 was extracted for rat brain nuclei by cation exchange chromatography; histone H1º was purified by gel filtration and the histones H1a, H1b, H1c and H1e were purified by reversed phase high performance liquid chromatography (RP-HPLC). CD spectra were performed in 10 mM phosphate buffer; 10 mM, 20% TFE phosphate buffer (trifluoroethanol); 10 mM, 40% TFE; phosphate buffer 10 mM, 60% TFE; phosphate buffer 10 mM, 150 mM NaCl and phosphate buffer 10 mm, 1 M NaCl. The analysis of the spectra was performed with JASCO Standard Analysis. Results: The percentage of alpha-helix was calculated using different mathematical methods, taking into account the molar ellipticity at 193 nm, and 222 nm, with K2D deconvolution program and the R1 and R2 qualitative relationships. The results indicate that TFE induced the alpha-helix structure in each of the subtypes, whereas NaCl did not induce any significant change. Conclusion: H1a and H1c are subtypes with highest content of alpha-helix. The observed differences in the percentage of alpha-helix between different subtypes may be important for their functional differentiation.
ABSTRACT
We recently developed an amphipathy scale, elaborated from molecular dynamics data that can be used for the identification of hydrophobic or hydrophilic regions in proteins. This amphipathy scale reflects side chain/water molecule interaction energies. We have now used this amphipathy scale to find candidates for transmembrane segments, by examining a large sample of membrane proteins with alpha-helix segments. The candidates were selected based on an amphipathy coefficient value range and the minimum number of residues in a segment. We compared our results with the transmembrane segments previously identified in the PDB_TM database by the TMDET algorithm. We expected that the hydrophobic segments would be identified using only the primary structures of the proteins and the amphipathy scale. However, some of these hydrophobic segments may pertain to hydrophobic pockets not included in transmembrane regions. We found that our amphipathy scale could identify alpha-helix transmembrane regions with a probability of success of 76% when all segments were included and 90% when all membrane proteins were included.
Subject(s)
Humans , Animals , Proteins/chemistry , Proteomics/methods , Amino Acids/chemistry , Sequence Analysis, Protein , Databases, Protein , Protein Conformation , Protein Structure, Secondary , Genetics , Proteins/metabolism , Computer SimulationABSTRACT
The structure and function of short-length amino terminal PTH analogues were studied. The substitution of Leu7 with Phe in [Ala3, 10Leu7Arg11]rPTH (1-11) NH2 analogue peptides did not show any reduction in cAMP formation. Replacement of the 1st, 7th and 8th residues revealed different activities, depending upon the residue type. The substitution of Ala1 by Ser in [Ala3, 10Leu7Arg11]rPTH (1-11) NH2 caused nearly a complete loss of cAMP formation. Meanwhile, NMR analysis of [ (Ala1/ Ser1) Ala3, 10 (Leu7/Phe7) Arg11]rPTH (1-11) NH2 revealed an alpha- helical backbone structure with a flexible conformation at the carboxyl-terminus. The overall results suggest that 11-residue short oligopeptide analogues of PTH tend to form an alpha-helical structure and the different activities of those analogues could be associated with residue specificity rather than the secondary conformational structure.