Here, we measured the concentrations of several ions in cultivated Gram-negative and Gram-positive bacteria, and analyzed their effects on polymer formation by the actin homologue MreB. We measured potassium, sodium, chloride, calcium and magnesium ion concentrations in Leptospira interrogans, Bacillus subtilis and Escherichia coli. Intracellular ionic strength contributed from these ions varied within the 130–273 mM range. The intracellular sodium ion concentration range was between 122 and 296 mM and the potassium ion concentration range was 5 and 38 mM. However, the levels were significantly influenced by extracellular ion levels. L. interrogans, Rickettsia rickettsii and E. coli MreBs were heterologously expressed and purified from E. coli using a novel filtration method to prepare MreB polymers. The structures and stability of Alexa-488 labeled MreB polymers, under varying ionic strength conditions, were investigated by confocal microscopy and MreB polymerization rates were assessed by measuring light scattering. MreB polymerization was fastest in the presence of monovalent cations in the 200–300 mM range. MreB filaments showed high stability in this concentration range and formed large assemblies of tape-like bundles that transformed to extensive sheets at higher ionic strengths. Changing the calcium concentration from 0.2 to 0 mM and then to 2 mM initialized rapid remodelling of MreB polymers.

Gelsolin is a severing and capping protein that targets filamentous actin and regulates filament lengths near plasma membranes, contributing to cell movement and plasma membrane morphology. Gelsolin binds to the plasma membrane via phosphatidylinositol 4,5-bisphosphate (PIP₂) in a state that cannot cap F-actin, and gelsolin-capped actin filaments are uncapped by PIP₂ leading to filament elongation. The process by which gelsolin is removed from PIP₂ at the plasma membrane is currently unknown. Gelsolin also binds ATP with unknown function. Here we characterize the role of ATP on PIP₂-gelsolin complex dynamics. Fluorophore-labeled PIP₂ and ATP were used to study their interactions with gelsolin using steady-state fluorescence anisotropy, and Alexa488-labeled gelsolin was utilized to reconstitute the regulation of gelsolin binding to PIP₂-containing phospholipid vesicles by ATP. Under physiological salt conditions ATP competes with PIP₂ for binding to gelsolin, while calcium causes the release of ATP from gelsolin. These data suggest a cycle for gelsolin activity. Firstly, calcium activates ATP-bound gelsolin allowing it to sever and cap F-actin. Secondly, PIP₂-binding removes the gelsolin cap from F-actin at low calcium levels, leading to filament elongation. Finally, ATP competes with PIP₂ to release the calcium-free ATP-bound gelsolin, allowing it to undergo a further round of severing.

Leiomodin proteins are vertebrate homologues of tropomodulin, having a role in the assembly and maintenance of muscle thin filaments. Leiomodin2 contains an N-terminal tropomodulin homolog fragment including tropomyosin-, and actin-binding sites, and a C-terminal Wiskott-Aldrich syndrome homology 2 actin-binding domain. The cardiac leiomodin2 isoform associates to the pointed end of actin filaments, where it supports the lengthening of thin filaments and competes with tropomodulin. It was recently found that cardiac leiomodin2 can localise also along the length of sarcomeric actin filaments. While the activities of leiomodin2 related to pointed end binding are relatively well described, the potential side binding activity and its functional consequences are less well understood. To better understand the biological functions of leiomodin2, in the present work we analysed the structural features and the activities of Rattus norvegicus cardiac leiomodin2 in actin dynamics by spectroscopic and high-speed sedimentation approaches. By monitoring the fluorescence parameters of leiomodin2 tryptophan residues we found that it possesses flexible, intrinsically disordered regions. Leiomodin2 accelerates the polymerisation of actin in an ionic strength dependent manner, which relies on its N-terminal regions. Importantly, we demonstrate that leiomodin2 binds to the sides of actin filaments and induces structural alterations in actin filaments. Upon its interaction with the filaments leiomodin2 decreases the actin-activated Mg²⁺-ATPase activity of skeletal muscle myosin. These observations suggest that through its binding to side of actin filaments and its effect on myosin activity leiomodin2 has more functions in muscle cells than it was indicated in previous studies.

According to the World Health Organization’s 2018 Global Cancer Survey, cancer is the second leading cause of death. From this survey, the third most common is breast cancer, the fifth is melanoma malignum and pancreatic adenocarcinoma ranks twentieth. Undoubtedly, the early diagnosis and monitoring of these tumors and related research is important for aspects of patient care. The aim of our present review was to explain an impressive methodology that is deemed suitable in reference to studying blood sample deviations in the case of solid tumors. Essentially, we compared the heat denaturation responses of blood plasma components through differential scanning calorimetry (DSC). In the control, between five and seven separable components can be detected, in which the primary component was albumin, while in the case of tumorous patients, the peaks of immunoglobulins were dominant. Moreover, the shape of the plasma DSC curves changed with a shift in the higher temperature ranges; thus, their pattern can be used as a suitable marker of direct immunological responses. The further development of the analysis of DSC curves raises the possibility of the early diagnosis of a potential tumor, the monitoring of diseases, or testing the efficacy of the therapy from a single drop of blood.