Phosphorylation of the carboxy-terminal domain of histone H1: effects on secondary structure and DNA condensation

Linker histone H1 plays an important role in chromatin folding. Phosphorylation by cyclin-dependent kinases is the main post-translational modification of histone H1. We studied the effects of phosphorylation on the secondary structure of the DNA-bound H1 carboxy-terminal domain (CTD), which contains most of the phosphorylation sites of the molecule. The effects of phosphorylation on the secondary structure of the DNA-bound CTD were site-specific and depended on the number of phosphate groups. Full phosphorylation significantly increased the proportion of β-structure and decreased that of α-helix. Partial phosphorylation increased the amount of undefined structure and decreased that of α-helix without a significant increase in β-structure. Phosphorylation had a moderate effect on the affinity of the CTD for the DNA, which was proportional to the number of phosphate groups. Partial phosphorylation drastically reduced the aggregation of DNA fragments by the CTD, but full phosphorylation restored to a large extent the aggregation capacity of the unphosphorylated domain. These results support the involvement of H1 hyperphosphorylation in metaphase chromatin condensation and of H1 partial phosphorylation in interphase chromatin relaxation. More generally, our results suggest that the effects of phosphorylation are mediated by specific structural changes and are not simply a consequence of the net charge

Model Systems of Precursor Cellular Membranes: Long-Chain Alcohols Stabilize Spontaneously Formed Oleic Acid Vesicles

AbstractOleic acid vesicles have been used as model systems to study the properties of membranes that could be the evolutionary precursors of more complex, stable, and impermeable phospholipid biomembranes. Pure fatty acid vesicles in general show high sensitivity to ionic strength and pH variation, but there is growing evidence that this lack of stability can be counterbalanced through mixtures with other amphiphilic or surfactant compounds. Here, we present a systematic experimental analysis of the oleic acid system and explore the spontaneous formation of vesicles under different conditions, as well as the effects that alcohols and alkanes may have in the process. Our results support the hypothesis that alcohols (in particular 10- to 14-C-atom alcohols) contribute to the stability of oleic acid vesicles under a wider range of experimental conditions. Moreover, studies of mixed oleic-acid-alkane and oleic-acid-alcohol systems using infrared spectroscopy and Langmuir trough measurements indicate that precisely those alcohols that increased vesicle stability also decreased the mobility of oleic acid polar headgroups, as well as the area/molecule of lipid

Epidemiological trends of HIV/HCV coinfection in Spain, 2015-2019

Altres ajuts: Spanish AIDS Research Network; European Funding for Regional Development (FEDER).Objectives: We assessed the prevalence of anti-hepatitis C virus (HCV) antibodies and active HCV infection (HCV-RNA-positive) in people living with HIV (PLWH) in Spain in 2019 and compared the results with those of four similar studies performed during 2015-2018. Methods: The study was performed in 41 centres. Sample size was estimated for an accuracy of 1%. Patients were selected by random sampling with proportional allocation. Results: The reference population comprised 41 973 PLWH, and the sample size was 1325. HCV serostatus was known in 1316 PLWH (99.3%), of whom 376 (28.6%) were HCV antibody (Ab)-positive (78.7% were prior injection drug users); 29 were HCV-RNA-positive (2.2%). Of the 29 HCV-RNA-positive PLWH, infection was chronic in 24, it was acute/recent in one, and it was of unknown duration in four. Cirrhosis was present in 71 (5.4%) PLWH overall, three (10.3%) HCV-RNA-positive patients and 68 (23.4%) of those who cleared HCV after anti-HCV therapy (p = 0.04). The prevalence of anti-HCV antibodies decreased steadily from 37.7% in 2015 to 28.6% in 2019 (p < 0.001); the prevalence of active HCV infection decreased from 22.1% in 2015 to 2.2% in 2019 (p < 0.001). Uptake of anti-HCV treatment increased from 53.9% in 2015 to 95.0% in 2019 (p < 0.001). Conclusions: In Spain, the prevalence of active HCV infection among PLWH at the end of 2019 was 2.2%, i.e. 90.0% lower than in 2015. Increased exposure to DAAs was probably the main reason for this sharp reduction. Despite the high coverage of treatment with direct-acting antiviral agents, HCV-related cirrhosis remains significant in this population

Advanced Techniques in Biophysics

Technical advancements are basic elements in our life. In biophysical studies, new applications and improvements in well-established techniques are being implemented every day. This book deals with advancements produced not only from a technical point of view, but also from new approaches that are being taken in the study of biophysical samples, such as nanotechniques or single-cell measurements. This book constitutes a privileged observatory for reviewing novel applications of biophysical techniques that can help the reader enter an area where the technology is progressing quickly and where a comprehensive explanation is not always to be found

Phosphorylation of the carboxy-terminal domain of histone H1 : effects on secondary structure and DNA condensation

Linker histone H1 plays an important role in chromatin folding. Phosphorylation by cyclin-dependent kinases is the main post-translational modification of histone H1. We studied the effects of phosphorylation on the secondary structure of the DNA-bound H1 carboxy-terminal domain (CTD), which contains most of the phosphorylation sites of the molecule. The effects of phosphorylation on the secondary structure of the DNA-bound CTD were site-specific and depended on the number of phosphate groups. Full phosphorylation significantly increased the proportion of β-structure and decreased that of α-helix. Partial phosphorylation increased the amount of undefined structure and decreased that of α-helix without a significant increase in β-structure. Phosphorylation had a moderate effect on the affinity of the CTD for the DNA, which was proportional to the number of phosphate groups. Partial phosphorylation drastically reduced the aggregation of DNA fragments by the CTD, but full phosphorylation restored to a large extent the aggregation capacity of the unphosphorylated domain. These results support the involvement of H1 hyperphosphorylation in metaphase chromatin condensation and of H1 partial phosphorylation in interphase chromatin relaxation. More generally, our results suggest that the effects of phosphorylation are mediated by specific structural changes and are not simply a consequence of the net charge

Methionine adenosyltransferase α-helix structure unfolds at lower temperatures than β-sheet: A 2D-IR study

Two-dimensional infrared spectroscopy has been used to characterize rat liver methionine adenosyltransferase and the events taking place during its thermal unfolding. Secondary structure data have been obtained for the native recombinant enzyme by fitting the amide I band of infrared spectra. Thermal denaturation studies allow the identification of events associated with individual secondary-structure elements during temperature-induced unfolding. They are correlated to the changes observed in enzyme activity and intrinsic fluorescence. In all cases, thermal denaturation proved to be an irreversible process, with a Tm of 47–51 C. Thermal profiles and two-dimensional infrared spectroscopy show that unfolding starts with a-helical segments and turns, located in the outer part of the protein, whereas extended structure, associated with subunit contacts, unfolds at higher temperatures. The data indicate a good correlation between the denaturation profiles obtained from activity measurements, fluorescence spectroscopy, and the behavior of the infrared bands. A study of the sequence of events that takes place is discussed in light of the previous knowledge on methionine adenosyltransferase structure and oligomerization pathway.This work was supported by grant BMC2002-01438 (Ministerio de Ciencia y Tecnología) and 9/UPV00042.310-13552 from Universidad del Pais Vasco. M.A.P. was supported by grant 01/1077 (Fondo de Investigación Sanitaria), grant BMC2002-00243 (Ministerio de Ciencia y Tecnología), and Red de Centros RCMN (C03/08).Peer reviewe

Differential interaction of equinatoxin II with model membranes in response to lipid composition

Copyright © by Biophysical Society. Final full-text version of the paper available at: http://www.biophysj.org/cgi/content/abstract/80/3/1343Equinatoxin II is a 179-amino-acid pore-forming protein isolated from the venom of the sea anemone Actinia equina. Large unilamellar vesicles and lipid monolayers of different lipid compositions have been used to study its interaction with membranes. The critical pressure for insertion is the same in monolayers made of phosphatidylcholine or sphingomyelin (;26 mN m21) and explains why the permeabilization of large unilamellar vesicles by equinatoxin II with these lipid compositions is null or moderate. In phosphatidylcholine-sphingomyelin (1:1) monolayers, the critical pressure is higher (;33 mN m21), thus permitting the insertion of equinatoxin II in large unilamellar vesicles, a process that is accompanied by major conformational changes. In the presence of vesicles made of phosphatidylcholine, a fraction of the protein molecules remains associated with the membranes. This interaction is fully reversible, does not involve major conformational changes, and is governed by the high affinity for membrane interfaces of the protein region comprising amino acids 101–120. We conclude that although the presence of sphingomyelin within the membrane creates conditions for irreversible insertion and pore formation, this lipid is not essential for the initial partitioning event, and its role as a specific receptor for the toxin is not so clear-cut.This work was supported by grants PI-1998–110 and UE-1998–43 from the Basque Government. J.M.M.C., I.E., and I.G.A. were recipients of predoctoral fellowships from the Basque Government.Peer reviewe

Differential interaction of equinatoxin II with model membranes in response to lipid composition

Copyright © by Biophysical Society. Final full-text version of the paper available at: http://www.biophysj.org/cgi/content/abstract/80/3/1343Equinatoxin II is a 179-amino-acid pore-forming protein isolated from the venom of the sea anemone Actinia equina. Large unilamellar vesicles and lipid monolayers of different lipid compositions have been used to study its interaction with membranes. The critical pressure for insertion is the same in monolayers made of phosphatidylcholine or sphingomyelin (;26 mN m21) and explains why the permeabilization of large unilamellar vesicles by equinatoxin II with these lipid compositions is null or moderate. In phosphatidylcholine-sphingomyelin (1:1) monolayers, the critical pressure is higher (;33 mN m21), thus permitting the insertion of equinatoxin II in large unilamellar vesicles, a process that is accompanied by major conformational changes. In the presence of vesicles made of phosphatidylcholine, a fraction of the protein molecules remains associated with the membranes. This interaction is fully reversible, does not involve major conformational changes, and is governed by the high affinity for membrane interfaces of the protein region comprising amino acids 101–120. We conclude that although the presence of sphingomyelin within the membrane creates conditions for irreversible insertion and pore formation, this lipid is not essential for the initial partitioning event, and its role as a specific receptor for the toxin is not so clear-cut.This work was supported by grants PI-1998–110 and UE-1998–43 from the Basque Government. J.M.M.C., I.E., and I.G.A. were recipients of predoctoral fellowships from the Basque Government.Peer reviewe