The end product of transglutaminase crosslinking: simultaneous quantitation of [Nepsilon-(gamma-glutamyl) lysine] and lysine by HPLC-MS3

Transglutaminse 2 and EGGL, the protein cross-link formed by transglutaminse 2, as therapeutic targets for disabilities of old age

Aging of the extracellular matrix (ECM), the protein matrix that surrounds and penetrates the tissues and binds the body together, contributes significantly to functional aging of tissues. ECM proteins become increasingly cross-linked with age, and this cross-linking is probably important in the decline of the ECM's function. This article reviews the role of ε-(γ-glutamyl)-lysine (EGGL), a cross-link formed by transglutaminase enzymes, and particularly the widely expressed isozyme transglutaminase 2 (TG2), in the aging ECM. There is little direct data on EGGL accumulation with age, and no direct evidence of a role of EGGL in the aging of the ECM with pathology. However, several lines of circumstantial evidence suggest that EGGL accumulates with age, and its association with pathology suggests that this might reflect degradation of ECM function. TG activity increases with age in many circumstances. ECM protein turnover is such that some EGGL made by TG is likely to remain in place for years, if not decades, in healthy tissue, and both EGGL and TG levels are enhanced by age-related diseases. If further research shows EGGL does accumulate with age, removing it could be of therapeutic benefit. Also reviewed is the blockade of TG and active removal of EGGL as therapeutic strategies, with the conclusion that both have promise. EGGL removal may have benefit for acute fibrotic diseases, such as tendinopathy, and for treating generalized decline in ECM function with old age. Extracellular TG2 and EGGL are therefore therapeutic targets both for specific and more generalized diseases of aging.

γ-Glutamylamines and neurodegenerative diseases

Transglutaminases catalyze the formation of γ-glutamylamines utilizing glutamyl residues and amine-bearing compounds such as lysyl residues and polyamines. These γ-glutamylamines can be released from proteins by proteases in an intact form. The free γ-glutamylamines can be catabolized to 5-oxo-L-proline and the free amine by γ-glutamylamine cyclotransferase. Free γ-glutamylamines, however, accumulate in the CSF and affected areas of Huntington Disease brain. This observation suggests transglutaminase-derived γ-glutamylamines may play a more significant role in neurodegeneration than previously thought. The following monograph reviews the metabolism of γ-glutamylamines and examines the possibility that these species contribute to neurodegeneration.

Development of a LC-ESI-MS3 method for determination of nitrendipine in human plasma

A novel and sensitive method utilizing high performance liquid chromatography coupled with electrospray ionization source tandem mass spectrometry (LC-ESI-MS(3)) was developed for the first time in order to analyze nitrendipine in human plasma samples. Human plasma samples were prepared by protein precipitation with acetonitrile and well resolved on a 100 mm reversed-phase column in gradient elution with 0.05% (v/v) formic acid in acetonitrile as the mobile phase. Determination was performed in MS(3) scan mode for nitrendipine and in the multiple reaction monitoring (MRM) mode for nimodipine (internal standard). This method, having a lower limit of quantification (LLOQ) of 0.05 ng/mL when using a 100 μL sample aliquot (5 pg/sample), is acceptable for calibration of the linearity and repeatability and is of better sensitivity than the reported methods (>0.25 ng/mL). The major advantages of the method are that small sample volume (100 μL) is required, simple sample processing technique, high sensitivity and excellent selectivity is guaranteed by the MS(3) detection. The proposed validated method has been successfully applied to a clinical study on nitrendipine.

Effect of protein structural integrity on cross-linking by tyrosinase evidenced by multidimensional heteronuclear magnetic resonance spectroscopy

Enzymatic cross-linking of proteins can be catalyzed either by transferase-type enzymes, e.g., transglutaminases, or by oxidoreductases, e.g., tyrosinases or laccases. Three-dimensional structure of protein substrate plays a key role in these reactions, that is, the reactivity and end product are strongly modulated by the accessibility of target amino acid residues to the cross-linking enzyme. Typically structural integrity of protein can be distorted by heat, pH, or mechanical action, as well as by varying ionic concentration of the solution. In this study we used partially unfolded protein (wild-type DrkN SH3) and its structurally stabilized mutant (T22G) to investigate the impact of folded/unfolded conformations on cross-linking by Trichoderma reesei tyrosinase. Our results clearly showed formation of intermolecular cross-links solely between unfolded conformations, making them superior substrates to folded proteins when using tyrosinase as a cross-linking enzyme. Multidimensional heteronuclear magnetic resonance experiments in solution state were employed to investigate cross-linked end-products. The results presented in this study form basis for application development in food, medical, cosmetic, textile, packing and other sectors. In addition, the outcome of this study has a high value for the basic understanding of reaction mechanism of tyrosinases on proteins.

Barnacle cement: a polymerization model based on evolutionary concepts

Enzymes and biochemical mechanisms essential to survival are under extreme selective pressure and are highly conserved through evolutionary time. We applied this evolutionary concept to barnacle cement polymerization, a process critical to barnacle fitness that involves aggregation and cross-linking of proteins. The biochemical mechanisms of cement polymerization remain largely unknown. We hypothesized that this process is biochemically similar to blood clotting, a critical physiological response that is also based on aggregation and cross-linking of proteins. Like key elements of vertebrate and invertebrate blood clotting, barnacle cement polymerization was shown to involve proteolytic activation of enzymes and structural precursors, transglutaminase cross-linking and assembly of fibrous proteins. Proteolytic activation of structural proteins maximizes the potential for bonding interactions with other proteins and with the surface. Transglutaminase cross-linking reinforces cement integrity. Remarkably, epitopes and sequences homologous to bovine trypsin and human transglutaminase were identified in barnacle cement with tandem mass spectrometry and/or western blotting. Akin to blood clotting, the peptides generated during proteolytic activation functioned as signal molecules, linking a molecular level event (protein aggregation) to a behavioral response (barnacle larval settlement). Our results draw attention to a highly conserved protein polymerization mechanism and shed light on a long-standing biochemical puzzle. We suggest that barnacle cement polymerization is a specialized form of wound healing. The polymerization mechanism common between barnacle cement and blood may be a theme for many marine animal glues.