Heparin Blocks the Inhibition of Tissue Kallikrein 1 by Kallistatin through Electrostatic Repulsion

Kallikrein-related peptidase's significance in Alzheimer's disease pathogenesis: A comprehensive survey

Alzheimer's disease (AD) and related dementias constitute an important global health challenge. Detailed understanding of the multiple molecular mechanisms underlying their pathogenesis constitutes a clue for the management of the disease. Kallikrein-related peptidases (KLKs), a lead family of serine proteases, have emerged as potential biomarkers and therapeutic targets in the context of AD and associated cognitive decline. Hence, KLKs were proposed to display multifaceted impacts influencing various aspects of neurodegeneration, including amyloid-beta aggregation, tau pathology, neuroinflammation, and synaptic dysfunction. We propose here a comprehensive survey to summarize recent findings, providing an overview of the main kallikreins implicated in AD pathophysiology namely KLK8, KLK6 and KLK7. We explore the interplay between KLKs and key AD molecular pathways, shedding light on their significance as potential biomarkers for early disease detection. We also discuss their pertinence as therapeutic targets for disease-modifying interventions to develop innovative therapeutic strategies aimed at halting or ameliorating the progression of AD and associated dementias.

A novel pathological mutant reveals the role of torsional flexibility in the serpin breach in adoption of an aggregation-prone intermediate

Mutants of alpha-1-antitrypsin cause the protein to self-associate and form ordered aggregates ('polymers') that are retained within hepatocytes, resulting in a predisposition to the development of liver disease. The associated reduction in secretion, and for some mutants, impairment of function, leads to a failure to protect lung tissue against proteases released during the inflammatory response and an increased risk of emphysema. We report here a novel deficiency mutation (Gly192Cys), that we name the Sydney variant, identified in a patient in heterozygosity with the Z allele (Glu342Lys). Cellular analysis revealed that the novel variant was mostly retained as insoluble polymers within the endoplasmic reticulum. The basis for this behaviour was investigated using biophysical and structural techniques. The variant showed a 40% reduction in inhibitory activity and a reduced stability as assessed by thermal unfolding experiments. Polymerisation involves adoption of an aggregation-prone intermediate and paradoxically the energy barrier for transition to this state was increased by 16% for the Gly192Cys variant with respect to the wild-type protein. However, with activation to the intermediate state, polymerisation occurred at a 3.8-fold faster rate overall. X-ray crystallography provided two crystal structures of the Gly192Cys variant, revealing perturbation within the 'breach' region with Cys192 in two different orientations: in one structure it faces towards the hydrophobic core while in the second it is solvent-exposed. This orientational heterogeneity was confirmed by PEGylation. These data show the critical role of the torsional freedom imparted by Gly192 in inhibitory activity and stability against polymerisation.

Kallistatin as an inhibitory protein against colorectal cancer cells through binding to LRP6

Kallistatin (KL) is a member of the serine proteinase inhibitor (serpin) family regulating oxidative stress, vascular relaxation, inflammation, angiogenesis, cell proliferation, and invasion. The heparin-binding site of Kallistatin has an important role in the interaction with LRP6 leading to the blockade of the Wnt signaling pathway. In this study, we aimed to explore the structural basis of the Kallistatin-LRP6E1E4 complex using in silico approaches and evaluating the anti-proliferative, apoptotic, and cell cycle arrest activities of Kallistatin in colon cancer lines. The molecular docking showed Kallistatin could bind to the LRP6E3E4 much stronger than LRP6E1E2. The Kallistatin-LRP6E1E2 and Kallistatin-LRP6E3E4 complexes were stable during Molecular Dynamics (MD) simulation. The Molecular Mechanics/Poisson-Boltzmann Surface Area (MM/PBSA) showed that the Kallistatin-LRP6E3E4 has a higher binding affinity compared to Kallistatin-LRP6E1E2. Kallistatin induced higher cytotoxicity and apoptosis in HCT116 compared to the SW480 cell line. This protein-induced cell-cycle arrest in both cell lines at the G1 phase. The B-catenin, cyclin D1, and c-Myc expression levels were decreased in response to treatment with Kallistatin in both cell lines while the LRP6 expression level was decreased in the HCT116 cell line. Kallistatin has a greater effect on the HCT116 cell line compared to the SW480 cell line. Kallistatin can be used as a cytotoxic and apoptotic-inducing agent in colorectal cancer cell lines.

The versatile role of Serpina3c in physiological and pathological processes: a review of recent studies

Murine Serpina3c belongs to the family of serine protease inhibitors (Serpins), clade "A" and its human homologue is SerpinA3. Serpina3c is involved in some physiological processes, including insulin secretion and adipogenesis. In the pathophysiological process, the deletion of Serpina3c leads to more severe metabolic disorders, such as aggravated non-alcoholic fatty liver disease (NAFLD), insulin resistance and obesity. In addition, Serpina3c can improve atherosclerosis and regulate cardiac remodeling after myocardial infarction. Many of these processes are directly or indirectly mediated by its inhibition of serine protease activity. Although its function has not been fully revealed, recent studies have shown its potential research value. Here, we aimed to summarize recent studies to provide a clearer view of the biological roles and the underlying mechanisms of Serpina3c.

DNA accelerates the protease inhibition of a bacterial serpin chloropin

Serine protease inhibitors (Serpins) are the most widely distributed protease inhibitors in nature and have been identified from all kingdoms of life. Eukaryotic serpins are most abundant with their activities often subject to modulation by cofactors; however, little is known about the regulation of prokaryotic serpins. To address this, here we prepared a recombinant bacteria serpin, termed chloropin, derived from green sulfur bacteria Chlorobium limicola and solved its crystal structure at 2.2 Å resolution. This showed a canonical inhibitory serpin conformation of native chloropin with a surface-exposed reactive loop and a large central beta-sheet. Enzyme activity analysis showed that chloropin could inhibit multiple proteases, such as thrombin and KLK7 with second order inhibition rate constants at 2.5×104 M−1s−1 and 4.5×104 M−1s−1 respectively, consistent with its P1 arginine residue. Heparin could accelerate the thrombin inhibition by ∼17-fold with a bell-shaped dose-dependent curve as seen with heparin-mediated thrombin inhibition by antithrombin. Interestingly, supercoiled DNA could accelerate the inhibition of thrombin by chloropin by 74-fold, while linear DNA accelerated the reaction by 142-fold through a heparin-like template mechanism. In contrast, DNA did not affect the inhibition of thrombin by antithrombin. These results indicate that DNA is likely a natural modulator of chloropin protecting the cell from endogenous or exogenous environmental proteases, and prokaryotic serpins have diverged during evolution to use different surface subsites for activity modulation.