Neprilysin is also known as skin fibroblast-derived elastase, and its up-regulation during aging is associated with impairments of the elastic fiber network, loss of skin elasticity and wrinkle formation. However, information on its elastase activity is still limited. The aim of this study was to investigate the degradation of fibrillar skin elastin by neprilysin and the influence of the donor's age on the degradation process using mass spectrometry and bioinformatics approaches. The results showed that cleavage by neprilysin is dependent on previous damage of elastin. While neprilysin does not cleave young and intact skin elastin well, it degrades elastin fibers from older donors, which may further promote aging processes. With regards to the cleavage behavior of neprilysin, a strong preference for Gly at P1 was found, while Gly, Ala and Val were well accepted at P1′ upon cleavage of tropoelastin and skin elastin. The results of the study indicate that the progressive release of bioactive elastin peptides by neprilysin upon skin aging may enhance local tissue damage and accelerate extracellular matrix aging processes.

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases worldwide. Formation of amyloid plaques consisting of amyloid-β peptides (Aβ) is one of the hallmarks of AD. Several lines of evidence have shown a correlation between the Aβ aggregation and the disease development. Extensive research has been conducted with the aim to reveal the structures of the neurotoxic Aβ aggregates. However, the exact structure of pathological aggregates and mechanism of the disease still remains elusive due to complexity of the occurring processes and instability of various disease-relevant Aβ species. In this article we review up-to-date structural knowledge about amyloid-β peptides, focusing on data acquired using solution and solid state NMR techniques. Furthermore, we discuss implications from these structural studies on the mechanisms of aggregation and neurotoxicity.

Skin aging is characterized by different features including wrinkling, atrophy of the dermis and loss of elasticity associated with damage to the extracellular matrix protein elastin. The aim of this study was to investigate the aging process of skin elastin at the molecular level by evaluating the influence of intrinsic (chronological aging) and extrinsic factors (sun exposure) on the morphology and susceptibility of elastin towards enzymatic degradation. Elastin was isolated from biopsies derived from sun-protected or sun-exposed skin of differently aged individuals. The morphology of the elastin fibers was characterized by scanning electron microscopy. Mass spectrometric analysis and label-free quantification allowed identifying differences in the cleavage patterns of the elastin samples after enzymatic digestion. Principal component analysis and hierarchical cluster analysis were used to visualize differences between the samples and to determine the contribution of extrinsic and intrinsic aging to the proteolytic susceptibility of elastin. Moreover, the release of potentially bioactive peptides was studied. Skin aging is associated with the decomposition of elastin fibers, which is more pronounced in sun-exposed tissue. Marker peptides were identified, which showed an age-related increase or decrease in their abundances and provide insights into the progression of the aging process of elastin fibers. Strong age-related cleavage occurs in hydrophobic tropoelastin domains 18, 20, 24 and 26. Photoaging makes the N-terminal and central parts of the tropoelastin molecules more susceptible towards enzymatic cleavage and, hence, accelerates the age-related degradation of elastin.

In contrast to the well characterized secreted phospholipases A2 (sPLA2) from animals, their homologues from plants have been less explored. Their production in purified form is more difficult, and no data on their stability are known. In the present paper, different variants of the sPLA2 isoform α from Arabidopsis thaliana (AtPLA2α) were designed using a new homology model with the aim to probe the impact of regions that are assumed to be important for stability and catalysis. Moreover tryptophan residues were introduced in critical regions to enable stability studies by fluorescence spectroscopy. The variants were expressed in Escherichia coli and the purified enzymes were analyzed to get first insights into the peculiarities of structure stability and structure activity relationships in plant sPLA2s in comparison with the well-characterized homologous enzymes from bee venom and porcine pancreas. Stability data of the AtPLA2 variants obtained by fluorescence or CD measurements of the reversible unfolding by guanidine hydrochloride and urea showed that all enzyme variants are less stable than the enzymes from animal sources although a similar tertiary core structure can be assumed based on molecular modeling. More extended loop structures at the N-terminus in AtPLA2α are suggested to be the main reasons for the much lower thermodynamic stabilities and cooperativities of the transition curves. Modifications in the N-terminal region (insertion, deletion, substitution by a Trp residue) exhibited a strong positive effect on activity whereas amino acid exchanges in other regions of the protein such as the Ca2+-binding loop and the loop connecting the two central helices were deleterious with respect to activity.

Jasmonates are ubiquitously occurring lipid-derived signaling compounds active in plant development and plant responses to biotic and abiotic stresses. Upon environmental stimuli jasmonates are formed and accumulate transiently. During flower and seed development, jasmonic acid (JA) and a remarkable number of different metabolites accumulate organ- and tissue specifically. The accumulation is accompanied with expression of jasmonate-inducible genes. Among these genes there are defense genes and developmentally regulated genes. The profile of jasmonate compounds in flowers and seeds covers active signaling molecules such as JA, its precursor 12-oxophytodienoic acid (OPDA) and amino acid conjugates such as JA-Ile, but also inactive signaling molecules occur such as 12-hydroxy-JA and its sulfated derivative. These latter compounds can occur at several orders of magnitude higher level than JA. Metabolic conversion of JA and JA-Ile to hydroxylated compounds seems to inactivate JA signaling, but also specific functions of jasmonates in flower and seed development were detected. In tomato OPDA is involved in embryo development. Occurrence of jasmonates, expression of JA-inducible genes and JA-dependent processes in flower and seed development will be discussed.

Over the past 200 years emissions of toxic heavy metals have risen tremendously and significantly exceed those from natural sources for practically all metals. Uptake and accumulation by crop plants represents the main entry pathway for potentially health-threatening toxic metals into human and animal food. Of major concern are the metalloids arsenic (As) and selenium (Se), and the metals cadmium (Cd), mercury (Hg), and lead (Pb). This review discusses the molecular mechanisms of toxic metal accumulation in plants and algae, the responses to metal exposure, as well as our understanding of metal tolerance and its evolution. The main emphasis will be on cadmium, which is by far the most widely studied of the non-essential toxic metals/metalloids. Entry via Zn2+, Fe2+, and Ca2+ transporters is the molecular basis of Cd2+ uptake into plant cells. Much less is known about the partitioning of non-essential metals and about the genes underlying the enormous diversity among plants with respect to Cd accumulation in different tissues. Numerous studies have described symptoms and responses of plants upon toxic metal exposure. Mysterious are primary targets of toxicity, the degree of specificity of responses, the sensing and the signaling events that lead to transcriptional activation. All plants apparently possess a basal tolerance of toxic non-essential metals. For Cd and As, this is largely dependent on the phytochelatin pathway. Not understood is the molecular biology of Cd hypertolerance in certain plant species such as the metallophytes Arabidopsis halleri or Thlaspi caerulescens.

Enol ethers are reacted with mercaptanes to give the corresponding O/S- or S/S-acetals in medium to high yield. Either product can be formed selectively depending on the acid catalyst and the reaction time applied.