Transglutaminases (Tgases) are a widely distributed group of enzymes that catalyse the post-translational modification of proteins by the formation of isopeptide bonds. This occurs either through protein cross-linking via epsilon-(gamma-glutamyl)lysine bonds or through incorporation of primary amines at selected peptide-bound glutamine residues. The cross-linked products, often of high molecular mass, are highly resistant to mechanical challenge and proteolytic degradation, and their accumulation is found in a number of tissues and processes where such properties are important, including skin, hair, blood clotting and wound healing. However, deregulation of enzyme activity generally associated with major disruptions in cellular homoeostatic mechanisms has resulted in these enzymes contributing to a number of human diseases, including chronic neurodegeneration, neoplastic diseases, autoimmune diseases, diseases involving progressive tissue fibrosis and diseases related to the epidermis of the skin. In the present review we detail the structural and regulatory features important in mammalian Tgases, with particular focus on the ubiquitous type 2 tissue enzyme. Physiological roles and substrates are discussed with a view to increasing and understanding the pathogenesis of the diseases associated with transglutaminases. Moreover the ability of these enzymes to modify proteins and act as biological glues has not gone unnoticed by the commercial sector. As a consequence, we have included some of the present and future biotechnological applications of this increasingly important group of enzymes.

The diatomic molecule of oxygen contains two uncoupled electrons and can therefore undergo reduction, yielding several different oxygen metabolites, which are collectively called Reactive Oxygen Species or ROS. They are invariably produced in aerobic environments through a variety of mechanisms, which include electron "leakage" during biologic oxidations, action of flavin dehydrogenases and specific membrane associated secretion, as well as by physical activation of oxygen by irradiation, e.g. UV sun-light. Organisms have developed efficient protective mechanisms against excessive accumulation of ROS, which include superoxide anion, hydrogen peroxide and hydroxyl radical, since all these metabolites are highly reactive and affect almost every kind of organism, either directly or through conversion into other derivatives, notably NO-derived radicals or RNS. Depending on their tissue concentration they can either exert beneficial physiologic effects (control of gene expression and mitogenesis) or damage cell structures, including lipids and membranes, proteins and nucleic acids, leading to cell death. In this brief overview we summarize the present state-of-the-art, restricting the discussion to the role of ROS in physiology and pathology, not taking into account RNS. Discussion will focus on basic chemical and biochemical features of ROS, underlining how ROS can promote severe diseases, including neoplastic, cardiovascular and neurodegenerative diseases. This brief discussion should clarify the present huge interest in ROS, in the perspective to develop new and specific therapeutic approaches.

The role of calcium ions in the regulation of tissue transglutaminase is investigated by experimental approaches and computer modeling. A three-dimensional model of the transglutaminase is computed by homology building on crystallized human factor XIII and is used to interpret structural and functional results. The molecule is a prolate ellipsoid (6.2 Â 4.2 Â 11 nm) and comprises four domains, assembled pairwise into N-terminal and C-terminal regions. The active site is hidden in a cleft between these regions and is inaccessible to macromolecular substrates in the calcium-free form. Protein dynamics simulation indicates that these regions move apart upon addition of calcium ions, revealing the active site for catalysis.The protein dimensions are consistent with results obtained with small-angle neutron and X-ray scattering. The gyration radius of the protein (3 nm) increases in the presence of calcium ions (3.9 nm), but it is virtually unaffected in the presence of GTP, suggesting that only calcium ions can promote major structural changes in the native protein.Proteolysis of an exposed loop connecting the N-terminal and C-terminal regions is linearly correlated with enzyme inactivation and prevents the calcium-induced conformational changes.

Our data showed that markers of oxidative challenge are associated with bone loss in women in post-menopausal status. We suggest that menopause-related estrogen withdrawal might contribute to make bone more vulnerable to oxidative injury thereby increasing the risk of PO development.

Calcium binding to erythrocyte transglutaminase was determined by equilibrium dialysis. Results indicate that 6 ions are bound to the enzyme both in the absence and in the presence of GTP and. that the nucleotide reduces the affinity of the enzyme for calcium. Furthermore, I-fluorescence quenching and proteolytic inactivation experiments proved that GTP also alters the conformation of the enzyme. It is thus suggested that multiple mechanisms are involved in the regulation of the enzyme activity by GTP.

A large body of evidences obtained in human and animal brain tissue suggest a role of oxidative stress (OxS) in the pathogenesis of late onset Alzheimer's disease (LOAD); on the contrary, data on peripheral markers of OxS in LOAD are still controversial. We evaluated the serum levels of products of lipid peroxidation, hydroperoxides, advanced oxidation protein products, total and residual antioxidant power, thiols, and uric acid in a sample of 334 older individuals: 101 LOAD patients, 134 patients with mild cognitive impairment (MCI), and 99 controls. At univariate analysis, serum hydroperoxides were higher while residual antioxidant power was lower in MCI and LOAD compared with in controls. By multivariate logistic regression analysis we found that, compared with controls, high levels (over median value) of serum hydroperoxides were independently associated with an increase in the likehood of having MCI (Odd Ratio: 2.59, 95% Confidence Interval: 1.08-6.21) or LOAD (OR: 4.09, 95%CI: 1.36-11.81). Furthermore, low levels of residual antioxidant power (below the median value) were associated with increased risk of having MCI (OR: 3.97, 95% CI: 1.62-9.72), but not dementia (OR: 2.31, 95%CI: 0.83-6.63). Our study suggests that a systemic redox-imbalance leading to OxS might be associated not only with LOAD but also with MCI.

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