Larvicidal potential of gold and silver nanoparticles synthesized using Acalypha fruticosa leaf extracts against Culex pipiens (Culicidae: Diptera)

Plant secondary metabolites have been recently used for the synthesis of different nanoparticles. The present investigation aimed at evaluating the effect of gold (AuNPs) and silver (AgNPs) nanoparticles synthesized using Acalypha fruticosa leaf extracts to control the mosquito Culex pipiens. The A. fruticosa AuNPs and AgNPs spectra displayed their maximum absorption at 550 nm and 440 nm, respectively. The infrared spectra revealed different functional groups related to different chemical compounds. The larval mortality of aqueous leaf extract of A. fruticosa was 499.54 ppm (LC₅₀) and 1734.06 ppm (LC₉₀) after 24 h of treatment. This study revealed that AuNP (LC₅₀, 30.2 and LC₉₀, 104.83 ppm) and AgNP (LC₅₀, 52.86 and LC₉₀, 157.227 ppm) preparations were highly effective compared to the A. fruticosa extract alone and also more affordable, as a smaller amount was required. The present findings show the potential larvicidal effect of the synthesized AuNPs and AgNPs for the control of mosquito-mediated disease transmission.     

Transient transfection of polarized epithelial monolayers with CFTR and reporter genes using efficacious lipids

Transient transfection of epithelial cells with lipid reagents has been limited because of toxicity and lack of efficacy. In this study, we show that more recently developed lipids transfect nonpolarized human airway epithelial cells with high efficacy and efficiency and little or no toxicity. Because of this success, we hypothesized that these lipids may also allow transient transfection of polarized epithelial monolayers. A panel of reagents was tested for transfer of the reporter gene luciferase (LUC) into polarized monolayers of non-cystic fibrosis (non-CF) and CF human bronchial epithelial cells, MDCK epithelial cell monolayers, and, ultimately, primary non-CF and CF airway epithelial cells. Lipid reagents, which were most successful in initial LUC assays, were also tested for transfer of vectors bearing the reporter gene green fluorescent protein (GFP) and for successful transfection and expression of an epithelial-specific protein, the cystic fibrosis transmembrane conductance regulator (CFTR). Electrophysiological, biochemical, and immunological assays were performed to show successful complementation of an epithelial monolayer with transiently expressed CFTR. We also present findings that help facilitate monolayer formation by these airway epithelial cell lines. Together, these data show that polarized monolayers are transfected transiently with more recently developed lipids, specifically LipofectAMINE PLUS and LipofectAMINE 2000. Transient transfection of epithelial monolayers provides a powerful system in which to express the cDNA of any epithelium-specific protein transiently in a native polarized epithelium to study protein function.     

Inhibition of the inositol trisphosphate receptor of mouse eggs and A7r5 cells by KN-93 via a mechanism unrelated to Ca2+/calmodulin-dependent protein kinase II antagonism

KN-93, a Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibitor, concentration-dependently and reversibly inhibited inositol 1,4,5-trisphosphate receptor (IP(3)R)-mediated [Ca(2+)](i) signaling in mouse eggs and permeabilized A7r5 smooth muscle cells, two cell types predominantly expressing type-1 IP(3)R (IP(3)R-1). KN-92, an inactive analog, was ineffective. The inhibitory action of KN-93 on Ca(2+) signaling depended neither on effects on IP(3) metabolism nor on the filling grade of Ca(2+) stores, suggesting a direct action on the IP(3)R. Inhibition was independent of CaMKII, since in identical conditions other CaMKII inhibitors (KN-62, peptide 281-309, and autocamtide-related inhibitory peptide) were ineffective and since CaMKII activation was precluded in permeabilized cells. Moreover, KN-93 was most effective in the absence of Ca(2+). Analysis of Ca(2+) release in A7r5 cells at varying [IP(3)], of IP(3)R-1 degradation in eggs, and of [(3)H]IP(3) binding in Sf9 microsomes all indicated that KN-93 did not affect IP(3) binding. Comparison of the inhibition of Ca(2+) release and of [(3)H]IP(3) binding by KN-93 and calmodulin (CaM), either separately or combined, was compatible with a specific interaction of KN-93 with a CaM-binding site on IP(3)R-1. This was also consistent with the much smaller effect of KN-93 in permeabilized 16HBE14o(-) cells that predominantly express type 3 IP(3)R, which lacks the high affinity CaM-binding site. These findings indicate that KN-93 inhibits IP(3)R-1 directly and may therefore be a useful tool in the study of IP(3)R functional regulation.     

State-dependent chemical reactivity of an engineered cysteine reveals conformational changes in the outer vestibule of the cystic fibrosis transmembrane conductance regulator

Cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels are gated by binding and hydrolysis of ATP at the nucleotide-binding domains (NBDs). We used covalent modification of CFTR channels bearing a cysteine engineered at position 334 to investigate changes in pore conformation that might accompany channel gating. In single R334C-CFTR channels studied in excised patches, modification by [2-(trimethylammonium)ethyl] methanethiosulfonate (MTSET+), which increases conductance, occurred only during channel closed states. This suggests that the rate of reaction of the cysteine was greater in closed channels than in open channels. R334C-CFTR channels in outside-out macropatches activated by ATP alone were modified with first order kinetics upon rapid exposure to MTSET+. Modification was much slower when channels were locked open by the addition of nonhydrolyzable nucleotide or when the R334C mutation was coupled to a second mutation, K1250A, which greatly decreases channel closing rate. In contrast, modification was faster in R334C/K464A-CFTR channels, which exhibit prolonged interburst closed states. These data indicate that the reactivity of the engineered cysteine in R334C-CFTR is state-dependent, providing evidence of changes in pore conformation coupled to ATP binding and hydrolysis at the NBDs. The data also show that maneuvers that lock open R334C-CFTR do so by locking channels into the prominent s2 subconductance state, suggesting that the most stable conducting state of the pore reflects the fully occupied, prehydrolytic state of the NBDs.     

Regulation of the phosphorylation of the inositol 1,4,5-trisphosphate receptor by protein kinase C

The various inositol 1,4,5-trisphosphate receptor (IP(3)R) isoforms are potential substrates for several protein kinases. We compared the in vitro phosphorylation of purified IP(3)R1 and IP(3)R3 by the catalytic subunit of protein kinase C (PKC). Phosphorylation of IP(3)R1 by PKC was about eight times stronger than that of IP(3)R3 under identical conditions. Protein kinase A strongly stimulated the PKC-induced phosphorylation of IP(3)R1. In contrast, Ca(2+) inhibited its phosphorylation (IC(50)相似文献   

Mutations at Arginine 352 Alter the Pore Architecture of CFTR

Arginine 352 (R352) in the sixth transmembrane domain of the cystic fibrosis transmembrane conductance regulator (CFTR) previously was reported to form an anion/cation selectivity filter and to provide positive charge in the intracellular vestibule. However, mutations at this site have nonspecific effects, such as inducing susceptibility of endogenous cysteines to chemical modification. We hypothesized that R352 stabilizes channel structure and that charge-destroying mutations at this site disrupt pore architecture, with multiple consequences. We tested the effects of mutations at R352 on conductance, anion selectivity and block by the sulfonylurea drug glipizide, using recordings of wild-type and mutant channels. Charge-altering mutations at R352 destabilized the open state and altered both selectivity and block. In contrast, R352K-CFTR was similar to wild-type. Full conductance state amplitude was similar to that of wild-type CFTR in all mutants except R352E, suggesting that R352 does not itself form an anion coordination site. In an attempt to identify an acidic residue that may interact with R352, we found that permeation properties were similarly affected by charge-reversing mutations at D993. Wild-type-like properties were rescued in R352E/D993R-CFTR, suggesting that R352 and D993 in the wild-type channel may interact to stabilize pore architecture. Finally, R352A-CFTR was sensitive to modification by externally applied MTSEA⁺, while wild-type and R352E/D993R-CFTR were not. These data suggest that R352 plays an important structural role in CFTR, perhaps reflecting its involvement in forming a salt bridge with residue D993.     

Quantitative MR measurements of regional and global left ventricular function and strain after intramyocardial transfer of VM202 into infarcted swine myocardium

Previous studies have shown the beneficial effects of the hepatocyte growth factor (HGF) gene on myocardial perfusion and infarction size but not on the regional strain in relationship to global left ventricular function. A noninvasive magnetic resonance (MR) study was performed to determine the effect of a new HGF gene, VM202, expressing two isoforms of HGF, on regional and global left ventricular function. Pigs (8/group) were divided into three groups: 1) controls without infarction; 2) reperfused, infarcted controls; and 3) infarcted, treated (1 h after reperfusion) with VM202 injected at eight sites. Cine, tagging, and delayed enhancement MR images were acquired at 3 and 50 +/- 3 days after infarction. At 50 days, ejection fraction in infarcted, treated animals increased (38 +/- 1% to 47 +/- 2%, P < 0.01) to the level of controls without infarction (52 +/- 1%, P = 0.16) but decreased in infarcted controls (41 +/- 1% to 37 +/- 1%, P < 0.05). Two-dimensional strain improved in remote, peri-infarcted, and infarcted myocardium. Furthermore, the infarction size was smaller in infarcted, treated animals (7.0 +/- 0.5%) compared with infarcted controls (13.2 +/- 1.6%, P < 0.05). Histopathology showed a lack of hypertrophy in myocytes in peri-infarcted and remote myocardium and the formation of islands/peninsulas of myocytes in infarcted, treated animals but not in infarcted controls. In conclusion, the plasmid HGF gene caused a near complete recovery of ejection fraction and improved the radial and circumferential strain of remote, peri-infarcted, and infarcted regions within 50 days. These beneficial effects may be explained by the combined effects of a speedy and significant infarct resorption and island/peninsulas of hypertrophied myocytes within the infarcted territory but not by compensatory hypertrophy. The combined use of cine and tagging MR imaging provides valuable information on the efficacy of gene therapy.     

The molecular evolution of function in the CFTR chloride channel

The ATP-binding cassette (ABC) transporter superfamily includes many proteins of clinical relevance, with genes expressed in all domains of life. Although most members use the energy of ATP binding and hydrolysis to accomplish the active import or export of various substrates across membranes, the cystic fibrosis transmembrane conductance regulator (CFTR) is the only known animal ABC transporter that functions primarily as an ion channel. Defects in CFTR, which is closely related to ABCC subfamily members that bear function as bona fide transporters, underlie the lethal genetic disease cystic fibrosis. This article seeks to integrate structural, functional, and genomic data to begin to answer the critical question of how the function of CFTR evolved to exhibit regulated channel activity. We highlight several examples wherein preexisting features in ABCC transporters were functionally leveraged as is, or altered by molecular evolution, to ultimately support channel function. This includes features that may underlie (1) construction of an anionic channel pore from an anionic substrate transport pathway, (2) establishment and tuning of phosphoregulation, and (3) optimization of channel function by specialized ligand–channel interactions. We also discuss how divergence and conservation may help elucidate the pharmacology of important CFTR modulators.

IntroductionThe ATP-binding cassette (ABC) transporter superfamily includes many members of clinical relevance, such as the multidrug resistance proteins (MRPs) and other proteins involved in generation of antibiotic resistance, transport of a wide variety of substrates in pathogenic bacteria, and transport of bile acids, lipids, and lipopolysaccharides (Ford and Beis, 2019; Jetter and Kullak-Ublick, 2020). ABC transporter genes encode the largest family of transmembrane (TM) proteins among living organisms (Briz et al., 2019) and are expressed in all domains of life (Ford and Beis, 2019; Holland et al., 2003). Either function or dysfunction of ABC transporters is implicated in development or treatment of cancer (Briz et al., 2019; Nobili et al., 2020), neurological disorders (Jha et al., 2019; Sumirtanurdin et al., 2019), detoxification (Briz et al., 2019), visual function (Garces et al., 2018), and, among many other clinical presentations (Moitra and Dean, 2011), in cystic fibrosis (CF; Riordan et al., 1989). In CF, mutations in the gene encoding CFTR lead to loss of anion transport in a wide variety of epithelial tissues (Csanády et al., 2019). In this review, we use the data generated from >30 yr of intensive structure-function study of CFTR and related proteins to propose and evaluate a potential route by which CFTR may have evolved unique function as a phosphorylation-regulated chloride channel. New insights are made possible by the advent of high-resolution cryo-EM structures of CFTR and the recent cloning and characterization of the evolutionarily oldest known orthologue of CFTR, from sea lamprey (Lp-CFTR; see below), which exhibits many functional differences from the human CFTR orthologue (hCFTR; Cui et al., 2019a).Overview of CFTRCFTR is a Cl⁻/HCO₃⁻ channel whose dysfunction directly leads to CF, the most common life-shortening genetic disease among Caucasians, affecting ∼80,000 individuals worldwide (Riordan et al., 1989; https://cftr2.org/mutations_history). The role of CFTR has been well characterized in airway, intestine, and sweat gland epithelial cells (Buchwald et al., 1991; Gonska et al., 2009; Haq et al., 2016; Quinton et al., 2012; Quinton, 2007; Trezíse and Buchwald, 1991), where the anionic flux mediated by the protein contributes to water secretion and regulation of pH (Pezzulo et al., 2012; Rowe et al., 2014). CFTR also functions in several nonepithelial cell types (Cook et al., 2016; Edlund et al., 2014; Gao and Su, 2015; Guo et al., 2014; Norez et al., 2014; Pohl et al., 2014; Schulz and Tümmler, 2016; Su et al., 2011), including in the brain (Ballerini et al., 2002; Guo et al., 2009; Hincke et al., 1995; Johannesson et al., 1997; Mulberg et al., 1995; Mulberg et al., 1998; Parkerson and Sontheimer, 2004; Pfister et al., 2015; Plog et al., 2010; Weyler et al., 1999). Several hundred disease-causing mutations have been identified in the CFTR gene. For a subset of these mutations, four small-molecule modulator therapeutics from Vertex Pharmaceuticals, Inc. that increase the surface expression or activity of CFTR have been approved for clinical use. The first approved drug, VX-770 (ivacaftor), is a gating potentiator that increases function of certain CFTR mutants (Cui et al., 2019b; Sosnay et al., 2013; Van Goor et al., 2009; Van Goor et al., 2014; Yu et al., 2012). A better understanding of these drugs and their binding sites may aid in refining the next class of therapeutics.ABC transporters use the energy of ATP binding and hydrolysis to accomplish the active import or export of various substrates across membranes (Rees et al., 2009). There are seven subfamilies of mammalian ABC transporters (ABCA, ABCB, ABCC,… ABCG), of which the E and F subfamilies do not bear actual transport function (Dean et al., 2001; Ford and Beis, 2019). A new classification of the ABC transporter superfamily that is based on the transmembrane domain (TMD) fold has recently been suggested (Thomas et al., 2020). CFTR is denoted ABCC7 and a member of type IV, respectively, according to these two classification schemes. CFTR bears ATPase activity like that of other ABCC subfamily members (Li et al., 1996; Stratford et al., 2007; Jordan et al., 2008), but biophysical methods have firmly established that CFTR functions as a phosphorylation-activated and ATP-gated ion channel (Anderson et al., 1991a; Anderson et al., 1991b; Bear et al., 1992; Berger et al., 1991; Sheppard et al., 1993), whereas its closest ABCC relatives function as multispecific exporters of organic anions (Jordan et al., 2008). CFTR may directly mediate the flux of glutathione (Gao et al., 1999; Kogan et al., 2003; Linsdell and Hanrahan, 1998), although CFTR-mediated active transport has not been shown, to our knowledge. Glutathione is transported by close ABCC relatives ABCC1/MRP1 (Mao et al., 1999) and ABCC4/MRP4 (Choi et al., 2001; Ko et al., 2002; Kogan et al., 2003; Ritter et al., 2005; Serrano et al., 2006); previous analysis has identified ABCC4 as CFTR’s closest relative (Jordan et al., 2008; see also Cui et al., 2019a). The domain organization of CFTR is similar to that of its closest relatives, the “short transporters” of the ABCC subfamily (Jordan et al., 2008; Ford and Beis, 2019; Srikant and Gaudet, 2019), with two nucleotide-binding domains (NBDs) that function in ATP binding and hydrolysis, and two TMDs, each containing six TM helices that comprise the substrate transport pathway (Fig. 1). However, unique to CFTR is an intracellular regulatory (R) domain that contains multiple consensus sites for phosphorylation by PKA (Sebastian et al., 2013).Open in a separate windowFigure 1.Domain architecture of CFTR. (A) Five functional domains: TMD1, NBD1, R domain with multiple phosphorylation sites, TMD2, and NBD2. Each TMD includes six transmembrane helices, numbered 1–12. The N-terminus includes the lasso motif (shown in pink), whereas the C-terminus includes a PDZ binding domain motif (yellow). (B) hCFTR from cryo-EM structure (PDB accession no. 6MSM). The R domain is not shown, because it is intrinsically unstructured.The opening of CFTR may be simplified to involve three sequential steps that have been uncovered via a combination of functional and structural data. First, PKA binds to (Mihályi et al., 2020) and phosphorylates (Rich et al., 1991) the aforementioned R domain, which results in loss of inhibitory interactions between that domain and the rest of the channel protein. Second, ATP binds to two sites at the interface of the cytoplasmic NBDs, which promotes a stable NBD dimer (Mense et al., 2006; Vergani et al., 2005). Finally, the wave of conformational changes associated with ATP-induced dimerization of the NBDs is transmitted to the pore domain, resulting in pore opening (Rahman et al., 2013; Simhaev et al., 2017; Sorum et al., 2015; Strickland et al., 2019). In related ABC exporters, ATP-dependent dimerization of the NBDs drives an overall transition from inward- to outward-facing conformation of the TMDs; this function was coopted by CFTR to drive ATP-induced channel opening (Fig. 2). At the level of individual residues, there is high conservation with transporters among amino acids in CFTR that are proposed to stabilize the inward-facing (closed) conformation in the absence of ATP (Wang et al., 2010; Wei et al., 2014; Wei et al., 2016), suggesting conservation of motifs integral to energetic signaling (Wang et al., 2014b; Wei et al., 2014; Wei et al., 2016). The close proximity of intracellular loops 2 and 4 (ICL2 and ICL4, respectively; Doshi et al., 2013; Wang et al., 2014b), constriction of the intracellular vestibule (Bai et al., 2011), and dilation of the extracellular vestibule, relative to the closed state, are all associated with channel opening (Beck et al., 2008; Infield et al., 2016; Norimatsu et al., 2012b; Rahman et al., 2013; Strickland et al., 2019). The CFTR pore opens in stages, requiring the sequential breaking and forming of intraprotein residue–residue interactions (Cui et al., 2013, 2014; Rahman et al., 2013), resulting in two subconductance states in addition to the full-conductance state (Gunderson and Kopito, 1995; Zhang et al., 2005a; Zhang et al., 2005b; Fig. 3). Using a particularly informative cysteine mutant at the outer vestibule, R334C-CFTR, the McCarty laboratory found that transitions between these subconductance states are highly dependent upon experimental conditions; for example, closing transitions almost always start from the s2 state in the presence of ATP, and transitions from s2 to f never occur in channels bound with the poorly hydrolyzable ATP analogue AMP-PNP (see also Langron et al., 2018), suggesting that this transition requires hydrolysis of nucleotide at the NBDs (Zhang et al., 2005a; Zhang et al., 2005b). Subconductance states are evident in recordings of WT CFTR from membrane patches and planar lipid bilayers, depending on experimental conditions, indicating that these represent inherent steps in gating of the channel pore (Gunderson and Kopito, 1995). In WT-hCFTR, this open pore is quite stable and does not close until ATP is hydrolyzed at the NBDs (Baukrowitz et al., 1994). Note that because CFTR displays three types of gating in one channel (phosphorylation-mediated, ligand-mediated, and pore-mediated gating), it serves as an exemplary target for studying the evolution of functional mechanisms within a single membrane protein.Open in a separate windowFigure 2.Hypothesis for emergence of channel function in CFTR. Modification of ATP-dependent transport activity in ABC transporters led to channel behavior, coopting the conformational changes necessary for unidirectional substrate transport in common ABC transporter systems. CFTR evolved features that break the alternating access cycle (solid-line arrows), enabling it to be open at both ends (box). Color scheme for major domains (again, lacking the R domain) is the same as in Fig. 1.Open in a separate windowFigure 3.Gating scheme for CFTR. Prephosphorylated channels are shown in the membrane (gray slab) with two TMDs (brown and dark blue) and two NBDs (green and light blue), with ATP (red circle) and ADP (yellow circle). ATP-dependent gating is shown as including NBD-mediated gating steps leading to pore gating between conductance levels. Here, we do not distinguish between s1 and s2 subconductance levels, because s1→s2 occurs very rapidly in WT-hCFTR.Natural history of the CFTR channel in vertebratesGiven the structural conservation among CFTR and ABC exporters noted above, and functional conservation in terms of ATP dependence, how CFTR evolved to function as an anion channel regulating passive ionic diffusion has been an enduring question (Srikant, 2020; Srikant et al., 2020). Molecular evolution studies are facilitated by the availability of many orthologues for the protein/gene of interest, spanning as much of the evolutionary record as possible. Currently, ∼300 CFTR orthologues are included in GenBank/UniProt, although not all of these are represented by expressible cDNA clones. Until very recently, the oldest CFTR orthologue known was from the dogfish shark, arising ∼150 million yr ago (MYA; Fig. 4; Marshall et al., 1991); this orthologue bears functional characteristics similar to those of hCFTR. However, reasoning that the identification of an earlier CFTR orthologue with altered structure/function would provide novel insight into the evolution of epithelial anion transport, the Gaggar and McCarty laboratories recently led an effort to clone and characterize the Lp-CFTR (Cui et al., 2019a), which arose ∼550 MYA (Smith et al., 2013). The identification of a CFTR orthologue in the jawless vertebrates establishes that CFTR exists across all vertebrates, predating the divergence of jawed and jawless vertebrates at the end of the Cambrian Period ∼488 MYA. Sequence analysis indicates 46% sequence identity and 65% sequence similarity between Lp-CFTR and hCFTR, which is much lower than that among jawed vertebrate CFTRs (jv-CFTRs) and includes surprising divergence in functionally relevant motifs. Accordingly, Lp-CFTR differs from hCFTR in multiple functional characteristics (Fig. 4). Thus, it cannot be automatically assumed that every position in CFTR that is unique in sea lamprey represents transitional change in the development of regulated channel activity. A good example in this regard is that of F508 in hCFTR, which is conserved across multiple ABC proteins but is leucine in lamprey (Cui et al., 2019a). Sorum et al. (2017) showed that replacing F508 with L in hCFTR significantly reduced its open probability. All known CFTRs other than Lp-CFTR and all known human ABCCs have F at this position, where the aromatic side chain is necessary for stabilizing the outward-facing state (Cui et al., 2006), so finding that this is substituted by a nonaromatic side chain in Lp-CFTR is mechanistically interesting and may represent a species-specific adaptation (Cui et al., 2019a).Open in a separate windowFigure 4.Simplified and truncated evolutionary tree for vertebrates. Green, common vertebrate ancestor; blue, jawless vertebrates; red and yellow, jawed vertebrates; yellow, mammals. CFTR orthologues studied in functional assays are shown underlined. (The time domain in this figure is not implied.)Table 1.Comparison of features between human and lamprey orthologues, focusing on three major domains of function: channel behavior, regulation, and modulation

Tight Functional Coupling of Kinesin-1A and Dynein Motors in the Bidirectional Transport of Neurofilaments

We have tested the hypothesis that kinesin-1A (formerly KIF5A) is an anterograde motor for axonal neurofilaments. In cultured sympathetic neurons from kinesin-1A knockout mice, we observed a 75% reduction in the frequency of both anterograde and retrograde neurofilament movement. This transport defect could be rescued by kinesin-1A, and with successively decreasing efficacy by kinesin-1B and kinesin-1C. In wild-type neurons, headless mutants of kinesin-1A and kinesin-1C inhibited both anterograde and retrograde movement in a dominant-negative manner. Because dynein is thought to be the retrograde motor for axonal neurofilaments, we investigated the effect of dynein inhibition on anterograde and retrograde neurofilament transport. Disruption of dynein function by using RNA interference, dominant-negative approaches, or a function-blocking antibody also inhibited both anterograde and retrograde neurofilament movement. These data suggest that kinesin-1A is the principal but not exclusive anterograde motor for neurofilaments in these neurons, that there may be some functional redundancy among the kinesin-1 isoforms with respect to neurofilament transport, and that the activities of the anterograde and retrograde neurofilament motors are tightly coordinated.