RESUMEN

HIV-1 assembly occurs at the plasma membrane, with the Gag polyprotein playing a crucial role. Gag association with the membrane is directed by the matrix domain (MA), which is myristoylated and has a highly basic region that interacts with anionic lipids. Several pieces of evidence suggest that the presence of phosphatidylinositol-(4,5)-bisphosphate (PIP2) highly influences this binding. Furthermore, MA also interacts with nucleic acids, which is proposed to be important for the specificity of GAG for PIP2-containing membranes. It is hypothesized that RNA has a chaperone function by interacting with the MA domain, preventing Gag from associating with unspecific lipid interfaces. Here, we study the interaction of MA with monolayer and bilayer membrane systems, focusing on the specificity for PIP2 and on the possible effects of a Gag N-terminal peptide on impairing the binding for either RNA or membrane. We found that RNA decreases the kinetics of the protein association with lipid monolayers but has no effect on the selectivity for PIP2. Interestingly, for bilayer systems, this selectivity increases in presence of both the peptide and RNA, even for highly negatively charged compositions, where MA alone does not discriminate between membranes with or without PIP2. Therefore, we propose that the specificity of MA for PIP2-containing membranes might be related to the electrostatic properties of both membrane and protein local environments, rather than a simple difference in molecular affinities. This scenario provides a new understanding of the regulation mechanism, with a macromolecular view, rather than considering molecular interactions within a ligand-receptor model.

Asunto(s)

RESUMEN

Specific protein-lipid interactions are critical for viral assembly. We present a molecular dynamics simulation study on the binding mechanism of the membrane targeting domain of HIV-1 Gag protein. The matrix (MA) domain drives Gag onto the plasma membrane through electrostatic interactions at its highly-basic-region (HBR), located near the myristoylated (Myr) N-terminus of the protein. Our study suggests Myr insertion is involved in the sorting of membrane lipids around the protein-binding site to prepare it for viral assembly. Our realistic membrane models confirm interactions with PIP2 and PS lipids are highly favored around the HBR and are strong enough to keep the protein bound even without Myr insertion. We characterized Myr insertion events from microsecond trajectories and examined the membrane response upon initial membrane targeting by MA. Insertion events only occur with one of the membrane models, showing a combination of surface charge and internal membrane structure modulate this process.

Asunto(s)

RESUMEN

The group-specific antigen (GAG) polyprotein of HIV-1 is the main coordinator of the virus assembly process at the plasma membrane (PM) and is directed by its N-terminal matrix domain (MA). MA is myristoylated and possess a highly basic region (HBR) responsible for the interaction with the negative lipids of the PM, especially with PIP2. In addition, MA binds RNA molecules proposed as a regulatory step of the assembly process. Here we study the interaction of a synthetic peptide (N-terminal 21 amino acids of MA) and liposomes of different compositions using a variety of biophysical techniques. Particularly, we use the fluorescence properties of the single tryptophan of the peptide to analyze its partition to membranes, where we harness for first time the analytical ability of spectral phasors method to study this interaction. We found that electrostatic interactions play an important role for peptide partition to membranes and myristoylation reduces the free energy of the process. Interestingly, we observe that while the presence of PIP2 does not cause measurable changes on the peptide-membrane interaction, the interaction is favored by cholesterol. Additionally, we found that the partition process goes through a transition state involving peptide disaggregation and changes in the peptide secondary structure. On the other hand, we found that the presence of oligonucleotides competes with the interaction with lipids by increasing peptide solubility. In summary, we think that our results, in context of the current knowledge of the role of HIV-1 MA, contribute to a better molecular understanding of the membrane association process.

Asunto(s)

RESUMEN

Human T-cell leukemia virus type 1 (HTLV-1) is the first retrovirus that has conclusively been shown to cause human diseases. In HIV-1, specific interactions between the nucleocapsid (NC) domain of the Gag protein and genomic RNA (gRNA) mediate gRNA dimerization and selective packaging; however, the mechanism for gRNA packaging in HTLV-1, a deltaretrovirus, is unclear. In other deltaretroviruses, the matrix (MA) and NC domains of Gag are both involved in gRNA packaging, but MA binds nucleic acids with higher affinity and has more robust chaperone activity, suggesting that this domain may play a primary role. Here, we show that the MA domain of HTLV-1, but not the NC domain, binds short hairpin RNAs derived from the putative gRNA packaging signal. RNA probing of the HTLV-1 5' leader and cross-linking studies revealed that the primer-binding site and a region within the putative packaging signal form stable hairpins that interact with MA. In addition to a previously identified palindromic dimerization initiation site (DIS), we identified a new DIS in HTLV-1 gRNA and found that both palindromic sequences bind specifically the NC domain. Surprisingly, a mutant partially defective in dimer formation in vitro exhibited a significant increase in RNA packaging into HTLV-1-like particles, suggesting that efficient RNA dimerization may not be strictly required for RNA packaging in HTLV-1. Moreover, the lifecycle of HTLV-1 and other deltaretroviruses may be characterized by NC and MA functions that are distinct from those of the corresponding HIV-1 proteins, but together provide the functions required for viral replication.

Asunto(s)

RESUMEN

The concept of a four-dimensional generalized difference matrix and its domain on some double sequence spaces was recently introduced and studied by Tug and Basar (AIP Conference Proceedings, vol. 1759, 2016) and Tug (J. Inequal. Appl. 2017(1):149, 2017). In this present paper, as a natural continuation of (J. Inequal. Appl. 2017(1):149, 2017), we introduce new almost null and almost convergent double sequence spaces [Formula: see text] and [Formula: see text] as the four-dimensional generalized difference matrix [Formula: see text] domain in the spaces [Formula: see text] and [Formula: see text], respectively. Firstly, we prove that the spaces [Formula: see text] and [Formula: see text] of double sequences are Banach spaces under some certain conditions. Then we give an inclusion relation of these new almost convergent double sequence spaces. Moreover, we identify the α-dual, [Formula: see text]-dual and γ-dual of the space [Formula: see text]. Finally, we characterize some new matrix classes [Formula: see text], [Formula: see text], and we complete this work with some significant results.

RESUMEN

In this paper, we introduce the binomial sequence spaces [Formula: see text], [Formula: see text] and [Formula: see text] by combining the binomial transformation and difference operator. We prove the BK-property and some inclusion relations. Furthermore, we obtain Schauder bases and compute the α-, ß- and γ-duals of these sequence spaces. Finally, we characterize matrix transformations on the sequence space [Formula: see text].

RESUMEN

The aim of this paper is to introduce the normed binomial sequence spaces [Formula: see text] by combining the binomial transformation and difference operator, where [Formula: see text]. We prove that these spaces are linearly isomorphic to the spaces [Formula: see text] and [Formula: see text], respectively. Furthermore, we compute Schauder bases and the α-, ß- and γ-duals of these sequence spaces.

RESUMEN

In this study, I introduce some new double sequence spaces [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] as the domain of four-dimensional generalized difference matrix [Formula: see text] in the spaces [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], respectively. I show that the double sequence spaces [Formula: see text], [Formula: see text] and [Formula: see text] are the Banach spaces under some certain conditions. I give some inclusion relations with some topological properties. Moreover, I determine the α-dual of the spaces [Formula: see text] and [Formula: see text], the [Formula: see text]-duals of the spaces [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], where [Formula: see text], and the γ-dual of the spaces [Formula: see text], [Formula: see text] and [Formula: see text]. Finally, I characterize the classes of four-dimensional matrix mappings defined on the spaces [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] of double sequences.

RESUMEN

The hepatitis B virus (HBV) is formed by budding. A stretch of 22 amino acids (aa) (matrix domain, MD, R103 - S124) in the large envelope protein L is crucial for virion formation and probably establishes contact to the nucleocapsid. Here, we assess the impact of sequence variations at numerous individual aa positions within the MD on virion formation. We generated panels of L mutants covering all 19 possible aa for 11 positions and tested the capacity of these mutants to rescue virus production by an L-defective HBV genome. At four positions (L112, R113, P117, W122), any replacement of the wild type (WT) aa reduced virus assembly to undetectable levels. Virus production was strongly diminished by substitutions at five other positions (R103, T106, S115, H116, A119). Only two tested positions (D114, Q118) tolerated several substitutions. The restricted positions may represent promising targets for the development of novel antiviral strategies.

Asunto(s)