Mechanical Operation and Intersubunit Coordination of Ring-Shaped Molecular Motors: Insights from Single-Molecule Studies

Ring NTPases represent a large and diverse group of proteins that couple their nucleotide hydrolysis activity to a mechanical task involving force generation and some type of transport process in the cell. Because of their shape, these enzymes often operate as gates that separate distinct cellular compartments to control and regulate the passage of chemical species across them. In this manner, ions and small molecules are moved across membranes, biopolymer substrates are segregated between cells or moved into confined spaces, double-stranded nucleic acids are separated into single strands to provide access to the genetic information, and polypeptides are unfolded and processed for recycling. Here we review the recent advances in the characterization of these motors using single-molecule manipulation and detection approaches. We describe the various mechanisms by which ring motors convert chemical energy to mechanical force or torque and coordinate the activities of individual subunits that constitute the ring. We also examine how single-molecule studies have contributed to a better understanding of the structural elements involved in motor-substrate interaction, mechanochemical coupling, and intersubunit coordination. Finally, we discuss how these molecular motors tailor their operation—often through regulation by other cofactors—to suit their unique biological functions.     

Personality,Relationship Conflict,and Teamwork-Related Mental Models

This study seeks to explore whether neuroticism, agreeableness, and conscientiousness moderate the influence of relationship conflict experienced in groups on changes in group members'' evaluative cognitions related to teamwork quality (teamwork-related mental models). Data from 216 students, nested in 48 groups were analyzed using a multilevel modeling approach. Our results show that the experience of relationship conflict leads to a negative shift from the pre-task to the post-task teamwork-related mental models. Moreover, the results indicate that conscientiousness buffered the negative association between relationship conflict and the change in teamwork-related mental models. Our results did not support the hypothesized moderating effect of agreeableness and show that the detrimental effect of relationship conflict on the shift in teamwork-related mental models is accentuated for group members scoring low rather than high on neuroticism. These findings open new research venues for exploring the association between personality, coping styles and change in teamwork-related mental models.     

Improved basal medium for Y-1 mouse adrenal cortex tumor cells in culture

Summary An improved basal medium is presented that requires only minimal supplementation with dialyzed fetal bovine serum or bovine serum albumin and fetuin to be comparable to Ham's F-10, which requires 15% horse serum (HS) and 2.5% fetal bovine serum (FBS) for the growth and function of Y-1, mouse adrenal cortex tumor, cells. Cell monolayers maintained for up to 2 weeks without any protein supplementation have retained their steroid response to ACTH. The medium differs from Ham's F-10 in its buffer composition and higher calcium-ion concentration. This medium should be a useful adjunct to studies pertaining to steroid and lipid intermediary metabolism, the retention of a specialized physiological function in a chemically defined medium, and the mechanism of hormonal response. Supported by the Medical Research Service of the Veterans Administration.     

6-hydroxy-l-nicotine from Arthrobacter nicotinovorans sustain spatial memory formation by decreasing brain oxidative stress in rats

Male Wistar rats were subjected to chronic 6-hydroxy-l-nicotine treatment (6HLN, 0.3 mg/kg, i.p., seven consecutive days) and their memory performance was studied by means of Y-maze and radial arm-maze tasks. 6HLN significantly increased spontaneous alternations in Y-maze task and working memory in radial arm-maze task, suggesting effects on short-term memory, without affecting long-term memory, explored by reference memory in radial arm-maze task. In addition, 6HLN increased antioxidant enzymes activity and decreased production of lipid peroxidation, suggesting antioxidant effects. Also, the linear regression between behavioral measures and oxidative stress markers resulted in significant correlations. Therefore, positive effects of 6HLN on spatial memory may occur by antioxidant actions.     

Comparative studies of water permeability of red blood cells from humans and over 30 animal species: an overview of 20 years of collaboration with Philip Kuchel

NMR measurements of the diffusional permeability of the human adult red blood cell (RBC) membrane to water (P _d) and of the activation energy (E _a,d) of the process furnished values of P _d ~ 4 × 10^?3 cm/s at 25 °C and ~6.1 × 10^?3 cm/s at 37 °C, and E _a,d ~ 26 kJ/mol. Comparative NMR measurements for other species showed: (1) monotremes (echidna and platypus), chicken, little penguin, and saltwater crocodile have the lowest P _d values; (2) sheep, cow, and elephant have P _d values lower than human P _d values; (3) cat, horse, alpaca, and camel have P _d values close to those of humans; (4) guinea pig, dog, dingo, agile wallaby, red-necked wallaby, Eastern grey kangaroo, and red kangaroo have P _d values higher than those of humans; (5) mouse, rat, rabbit, and “small and medium size” marsupials have the highest values of P _d (>8.0 × 10^?3 cm/s at 25 °C and >10.0 × 10^?3 cm/s at 37 °C). There are peculiarities of E _a,d values for the RBCs from different species. The maximum inhibition of diffusional permeability of RBCs induced by incubation with p-chloromercuribenzene sulfonate varied between 0 % (for the chicken and little penguin) to ~50 % (for human, mouse, cat, sheep, horse, camel, and Indian elephant), and ~60–75 % (for rat, guinea pig, rabbit, dog, alpaca, and all marsupials). These results indicate that no water channel proteins (WCPs) or aquaporins are present in the membrane of RBCs from monotremes (echidna, platypus), chicken, little penguin and saltwater crocodile whereas WCPs from the membranes of RBCs from marsupials have peculiarities.     

The 1H NMR Profile of Healthy Dog Cerebrospinal Fluid

The availability of data for reference values in cerebrospinal fluid for healthy humans is limited due to obvious practical and ethical issues. The variability of reported values for metabolites in human cerebrospinal fluid is quite large. Dogs present great similarities with humans, including in cases of central nervous system pathologies. The paper presents the first study on healthy dog cerebrospinal fluid metabolomic profile using ¹H NMR spectroscopy. A number of 13 metabolites have been identified and quantified from cerebrospinal fluid collected from a group of 10 mix breed healthy dogs. The biological variability as resulting from the relative standard deviation of the physiological concentrations of the identified metabolites had a mean of 18.20% (range between 9.3% and 44.8%). The reported concentrations for metabolites may be used as normal reference values. The homogeneity of the obtained results and the low biologic variability show that the ¹H NMR analysis of the dog’s cerebrospinal fluid is reliable in designing and interpreting clinical and therapeutic trials in dogs with central nervous system pathologies.     

Age‐related ultrastructural changes of the basement membrane in the mouse blood‐brain barrier

The blood‐brain barrier (BBB) is essential for a functional neurovascular unit. Most studies focused on the cells forming the BBB, but very few studied the basement membrane (BM) of brain capillaries in ageing. We used transmission electron microscopy and electron tomography to investigate the BM of the BBB in ageing C57BL/6J mice. The thickness of the BM of the BBB from 24‐month‐old mice was double as compared with that of 6‐month‐old mice (107 nm vs 56 nm). The aged BBB showed lipid droplets gathering within the BM which further increased its thickness (up to 572 nm) and altered its structure. The lipids appeared to accumulate toward the glial side of the BM. Electron tomography showed that the lipid‐rich BM regions are located in small pockets formed by the end‐feet of astrocytes. These findings suggest an imbalance of the lipid metabolism and that may precede the structural alteration of the BM. These alterations may favour the accretion of abnormal proteins that lead to neurodegeneration in ageing. These findings warrant further investigation of the BM of brain capillaries and of adjoining cells as potential targets for future therapies.     

The first water channel protein (later called aquaporin 1) was first discovered in Cluj-Napoca, Romania.

This invited review briefly outlines the importance of membrane water permeability, highlights the landmarks leading to the discovery of water channels. After a decade of systematic studies on water channels in human RBC Benga's group discovered in 1985 the presence and location of the water channel protein among the polypeptides migrating in the region of 35-60 kDa on the electrophoretogram of RBC membrane proteins. The work was extended and reviewed in several articles. In 1988, Agre and coworkers isolated a new protein from the RBC membrane, nick-named CHIP28 (channel-forming integral membrane protein of 28 kDa). However, in addition to the 28 kDa component, this protein had a 35-60 kDa glycosylated component, the one detected by the Benga's group. Only in 1992 Agre's group suggested that "it is likely that CHIP28 is a functional unit of membrane water channels". Half of the 2003 Nobel Prize in Chemistry was awarded to Peter Agre (Johns Hopkins University, Baltimore, USA) "for the discovery of water channels", actually the first water channel protein from the human red blood cell (RBC) membrane, known today as aquaporin 1 (AQP1). The seminal contributions from 1986 of the Benga's group were grossly overlooked by Peter Agre and by the Nobel Prize Committee. Thousands of science-related professionals from hundreds of academic and research units, as well as participants in several international scientific events, have signed as supporters of Benga; his priority is also mentioned in several comments on the 2003 Nobel Prize.     

Simulating the embolization of blood vessels using magnetic microparticles and acupuncture needle in a magnetic field

Computer models were developed to simulate the capture and subsequent deposition of magnetic microparticles (MMPs) in a blood vessel adjacent to a ferromagnetic wire (e.g., acupuncture needle) magnetized by a uniform external magnetic field. Process parameter conditions were obtained to enable optimal capture of MMPs into the deposit. It was found that the maximum capture distance of the MMPs was within 0.5-2.0 mm when the particles were superparamagnetic and had large size (>1.0 microm) and relative large flow rates (2.5-5.0 cm/s) as in a healthy artery. It was also found that the deposits were asymmetrical and that their size was between 1.0 and 2.0 mm. For the case of lower flow rates as can be found in a tumor (<1.0 mm/s) and using small magnetite particles (0.25-2.0 microm) the maximum capture distance was larger, ranging between approximately 0.5 and 6.4 mm, depending on the blood flow rate, the radius of wire, and particle clustering. The range of embolization (deposition) in this later case was between 0.5 and 5.9 mm. The potential of this technique to generate MMPs deposits to embolize blood vessels inhibiting the blood supply and thus facilitating necrosis of tumors located deep within the patient (3-7 cm) is discussed.