Mechano-transduction: from molecules to tissues.

External forces play complex roles in cell organization, fate, and homeostasis. Changes in these forces, or how cells respond to them, can result in abnormal embryonic development and diseases in adults. How cells sense and respond to these mechanical stimuli requires an understanding of the biophysical principles that underlie changes in protein conformation and result in alterations in the organization and function of cells and tissues. Here, we discuss mechano-transduction as it applies to protein conformation, cellular organization, and multi-cell (tissue) function

Photosensitivity reaction from operating room lights after oral administration of 5-aminolevulinic acid for fluorescence-guided resection of a malignant glioma

Orally administered 5-aminolevulinic acid (5-ALA), which was approved in the United States in 2017, is preferentially metabolized by malignant glioma cells into protoporphyrin IX and enhances tumor visualization when using a blue light filter on an operating microscope. Photosensitivity after 5-ALA administration is a known side effect, but a photosensitivity reaction from operating room lights has not yet been documented. We report the case of a 56-year-old man with a history of previous resection of a grade II astrocytoma who presented with imaging concerning for tumor recurrence and possible malignant transformation. Repeat surgical resection utilized 5-ALA. Soon after the surgery, he developed reddening of his skin, particularly over the right side of his head and neck, with blistering and peeling in a distribution that was particularly exposed to operating room lights during surgery. No other areas of his skin experienced the same redness, blistering, or peeling. Topical lotions were applied and the skin changes resolved spontaneously over weeks. Significant photosensitivity after administration of oral 5-ALA is a rare complication, but neurosurgeons who perform fluorescence-guided tumor resection should remain cognizant of its potential association with exposure to intense light, including in the operating room. Phototoxicity typically is self-limited, but awareness is important to minimize its occurrence

Eaten alive: cannibalism is enhanced by parasites

Cannibalism is ubiquitous in nature and especially pervasive in consumers with stage-specific resource utilization in resource-limited environments. Cannibalism is thus influential in the structure and functioning of biological communities. Parasites are also pervasive in nature and, we hypothesize, might affect cannibalism since infection can alter host foraging behaviour. We investigated the effects of a common parasite, the microsporidian Pleistophora mulleri, on the cannibalism rate of its host, the freshwater amphipod Gammarus duebeni celticus. Parasitic infection increased the rate of cannibalism by adults towards uninfected juvenile conspecifics, as measured by adult functional responses, that is, the rate of resource uptake as a function of resource density. This may reflect the increased metabolic requirements of the host as driven by the parasite. Furthermore, when presented with a choice, uninfected adults preferred to cannibalize uninfected rather than infected juvenile conspecifics, probably reflecting selection pressure to avoid the risk of parasite acquisition. By contrast, infected adults were indiscriminate with respect to infection status of their victims, probably owing to metabolic costs of infection and the lack of risk as the cannibals were already infected. Thus parasitism, by enhancing cannibalism rates, may have previously unrecognized effects on stage structure and population dynamics for cannibalistic species and may also act as a selective pressure leading to changes in resource use

Probing the heme-thiolate oxygenase domain of inducible nitric oxide synthase with Ru(II) and Re(I) electron tunneling wires

Nitric oxide synthase (NOS) catalyzes the production of nitric oxide from L-arginine and dioxygen at a thiolate-ligated heme active site. Although many of the reaction intermediates are as yet unidentified, it is well established that the catalytic cycle begins with substrate binding and rate-limiting electron transfer to the heme. Here, we show that Ru(II)-diimine and Re(I)-diimine electron tunneling wires trigger nanosecond photoreduction of the active-site heme in the enzyme. Very rapid generation of a reduced thiolate-ligated heme opens the way for direct observation of short-lived intermediates in the NOS reaction cycle

Nanosecond photoreduction of inducible nitric oxide synthase by a Ru-diimine electron tunneling wire bound distant from the active site

A Ru-diimine wire, [(4,4′,5,5′-tetramethylbipyridine)_2Ru(F_9bp)]^(2+) (tmRu-F_9bp, where F_9bp is 4-methyl-4′-methylperfluorobiphenylbipyridine), binds tightly to the oxidase domain of inducible nitric oxide synthase (iNOSoxy). The binding of tmRu-F_9bp is independent of tetrahydrobiopterin, arginine, and imidazole, indicating that the wire resides on the surface of the enzyme, distant from the active-site heme. Photoreduction of an imidazole-bound active-site heme iron in the enzyme-wire conjugate (k_(ET) = 2(1) × 10^7 s^(−1)) is fully seven orders of magnitude faster than the in vivo process

Electron tunneling through sensitizer wires bound to proteins

We report a quantitative theoretical analysis of long-range electron transfer through sensitizer wires bound in the active-site channel of cytochrome P450cam. Each sensitizer wire consists of a substrate group with high binding affinity for the enzyme active site connected to a ruthenium-diimine through a bridging aliphatic or aromatic chain. Experiments have revealed a dramatic dependence of electron transfer rates on the chemical composition of both the bridging group and the substrate. Using combined molecular dynamics simulations and electronic coupling calculations, we show that electron tunneling through perfluorinated aromatic bridges is promoted by enhanced superexchange coupling through virtual reduced states. In contrast, electron flow through aliphatic bridges occurs by hole-mediated superexchange. We have found that a small number of wire conformations with strong donor–acceptor couplings can account for the observed electron tunneling rates for sensitizer wires terminated with either ethylbenzene or adamantane. In these instances, the rate is dependent not only on electronic coupling of the donor and acceptor but also on the nuclear motion of the sensitizer wire, necessitating the calculation of average rates over the course of a molecular dynamics simulation. These calculations along with related recent findings have made it possible to analyze the results of many other sensitizer-wire experiments that in turn point to new directions in our attempts to observe reactive intermediates in the catalytic cycles of P450 and other heme enzymes

A mutli-technique search for the most primitive CO chondrites

As part of a study to identify the most primitive COs and to look for weakly altered CMs amongst the COs, we have conducted a multi-technique study of 16 Antarctic meteorites that had been classified as primitive COs. For this study, we have determined: (1) the bulk H, C and N abundances and isotopes, (2) bulk O isotopic compositions, (3) bulk modal mineralogies, and (4) for some selected samples the abundances and compositions of their insoluble organic matter (IOM). Two of the 16 meteorites do appear to be CMs – BUC 10943 seems to be a fairly typical CM, while MIL 090073 has probably been heated. Of the COs, DOM 08006 appears to be the most primitive CO identified to date and is quite distinct from the other members of its pairing group. The other COs fall into two groups that are less primitive than DOM 08006 and ALH 77307, the previously most primitive CO. The first group is composed of members of the DOM 08004 pairing group, except DOM 08006. The second group is composed of meteorites belonging to the MIL 03377 and MIL 07099 pairing groups. These two pairing groups should probably be combined. There is a dichotomy in the bulk O isotopes between the primitive (all Antarctic finds) and the more metamorphosed COs (mostly falls). This dichotomy can only partly be explained by the terrestrial weathering experienced by the primitive Antarctic samples. It seems that the more equilibrated samples interacted to a greater extent with 16O-poor material, probably water, than the more primitive meteorites

Kinisi:Bayesian analysis of mass transport from molecular dynamics simulations

kinisi is a Python package for estimating transport coefficients—e.g., self-diffusion coefficients, ∗—and their corresponding uncertainties from molecular dynamics simulation data. It includes an implementation of the approximate Bayesian regression scheme described in McCluskey etal. (2023), wherein the mean-squared displacement (MSD) of mobile atoms is modelled as a multivariate normal distribution that is parametrised from the input simulation data. kinisi uses Markov-chain Monte Carlo (Foreman-Mackey et al., 2019; Goodman &amp; Weare, 2010) to sample this model multivariate normal distribution to give a posterior distribution of linear model ensemble MSDs that are compatible with the observed simulation data. For each linear ensemble MSD, x(), a corresponding estimate of the diffusion coefficient, ̂∗ is given via the Einstein relation, ̂∗ =1d x() / 6 d where is time. The posterior distribution of compatible model ensemble MSDs calculated by kinisi gives a point estimate for the most probable value of ∗ , given the observed simulation data, and an estimate of the corresponding uncertainty in ̂∗. kinisi also provides equivalent functionality for estimating collective transport coefficients, i.e., jump-diffusion coefficients and ionic conductivities<br/