Fabrication of Insoluble Elastin by Enzyme-Free Cross-Linking

Elastin is an essential extracellular matrix protein that enables tissues and organs such as arteries, lungs, and skin, which undergo continuous deformation, to stretch and recoil. Here, an approach to fabricating artificial elastin with close-to-native molecular and mechanical characteristics is described. Recombinantly produced tropoelastin are polymerized through coacervation and allysine-mediated cross-linking induced by pyrroloquinoline quinone (PQQ). A technique that allows the recovery and repeated use of PQQ for protein cross-linking by covalent attachment to magnetic Sepharose beads is developed. The produced material closely resembles natural elastin in its molecular, biochemical, and mechanical properties, enabled by the occurrence of the cross-linking amino acids desmosine, isodesmosine, and merodesmosine. It possesses elevated resistance against tryptic proteolysis, and its Young's modulus ranging between 1 and 2 MPa is similar to that of natural elastin. The approach described herein enables the engineering of mechanically resilient, elastin-like materials for biomedical applications.

Dual Hydrazine-Equipped Turn-On Manganese-Based Probes for Magnetic Resonance Imaging of Liver Fibrogenesis

Liver fibrogenesis is accompanied by upregulation of lysyl oxidase enzymes, which catalyze oxidation of lysine ε-amino groups on the extracellular matrix proteins to form the aldehyde containing amino acid allysine (LysAld). Here, we describe the design and synthesis of novel manganese-based MRI probes with high signal amplification for imaging liver fibrogenesis. Rational design of a series of stable hydrazine-equipped manganese MRI probes gives Mn-2CHyd with the highest affinity and turn-on relaxivity (4-fold) upon reaction with LysAld. A dynamic PET-MRI study using [52Mn]Mn-2CHyd showed low liver uptake of the probe in healthy mice. The ability of the probe to detect liver fibrogenesis was then demonstrated in vivo in CCl4-injured mice. This study enables further development and application of manganese-based hydrazine-equipped probes for imaging liver fibrogenesis.

Acetylation, Methylation and Allysine Modification Profile of Viral and Host Proteins during Influenza A Virus Infection

Protein modifications dynamically occur and regulate biological processes in all organisms. Towards understanding the significance of protein modifications in influenza virus infection, we performed a global mass spectrometry screen followed by bioinformatics analyses of acetylation, methylation and allysine modification in human lung epithelial cells in response to influenza A virus infection. We discovered 8 out of 10 major viral proteins and 245 out of 2280 host proteins detected to be differentially modified by three modifications in infected cells. Some of the identified proteins were modified on multiple amino acids residues and by more than one modification; the latter occurred either on different or same residues. Most of the modified residues in viral proteins were conserved across >40 subtypes of influenza A virus, and influenza B or C viruses and located on the protein surface. Importantly, many of those residues have already been determined to be critical for the influenza A virus. Similarly, many modified residues in host proteins were conserved across influenza A virus hosts like humans, birds, and pigs. Finally, host proteins undergoing the three modifications clustered in common functional networks of metabolic, cytoskeletal, and RNA processes, all of which are known to be exploited by the influenza A virus.

Allysine and α-Aminoadipic Acid as Markers of the Glyco-Oxidative Damage to Human Serum Albumin under Pathological Glucose Concentrations

Understanding the molecular basis of the disease is of the utmost scientific interest as it contributes to the development of targeted strategies of prevention, diagnosis, and therapy. Protein carbonylation is a typical feature of glyco-oxidative stress and takes place in health disorders such as diabetes. Allysine as well as its oxidation product, the α-amino adipic acid (α-AA) have been found to be markers of diabetes risk whereas little is known about the chemistry involved in its formation under hyperglycemic conditions. To provide insight into this issue, human serum albumin was incubated in the presence of FeCl3 (25 μM) and increasing glucose concentrations for 32 h at 37 °C. These concentrations were selected to simulate (i) physiological fasting plasma concentration (4 mM), (ii) pathological pre-diabetes fasting plasma concentration (8 mM), and pathological diabetes fasting plasma concentration (12 mM) of glucose. While both allysine and α-AA were found to increase with increasing glucose concentrations, the carboxylic acid was only detected at pathological glucose concentrations and appeared to be a more reliable indicator of glyco-oxidative stress. The underlying chemical mechanisms of lysine glycation as well as of the depletion of tryptophan and formation of fluorescent and colored advanced glycation products are discussed.

Molecular Magnetic Resonance Imaging of Lung Fibrogenesis with an Oxyamine-Based Probe

Fibrogenesis is the active production of extracellular matrix in response to tissue injury. In many chronic diseases persistent fibrogenesis results in the accumulation of scar tissue, which can lead to organ failure and death. However, no non-invasive technique exists to assess this key biological process. All tissue fibrogenesis results in the formation of allysine, which enables collagen cross-linking and leads to tissue stiffening and scar formation. We report herein a novel allysine-binding gadolinium chelate (GdOA), that can non-invasively detect and quantify the extent of fibrogenesis using magnetic resonance imaging (MRI). We demonstrate that GdOA signal enhancement correlates with the extent of the disease and is sensitive to a therapeutic response.

A Genetically Encoded Allysine for the Synthesis of Proteins with Site-Specific Lysine Dimethylation

Using the amber suppression approach, N^ϵ -(4-azidobenzoxycarbonyl)-δ,ϵ-dehydrolysine, an allysine precursor is genetically encoded in E. coli. Its genetic incorporation followed by two sequential biocompatible reactions allows convenient synthesis of proteins with site-specific lysine dimethylation. Using this approach, dimethyl-histone H3 and p53 proteins have been synthesized and used to probe functions of epigenetic enzymes including histone demethylase LSD1 and histone acetyltransferase Tip60. We confirmed that LSD1 is catalytically active toward H3K4me2 and H3K9me2 but inert toward H3K36me2, and methylation at p53 K372 directly activates Tip60 for its catalyzed acetylation at p53 K120.