The role of esterification on detection of protonated and deprotonated peptide ions in matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS)

Hydrolyzed collagen: Exploring its applications in the food and beverage industries and assessing its impact on human health - A comprehensive review

Hydrolyzed collagen (HC) consists of many small and low-molecular-weight amino acid chains (3-6 kDa) that can be produced either in basic or acidic media through enzymatic activity. This review details the sources of hydrolyzed collagen, its biosynthesis and its uses in the food industry, as well as its production process and beneficial health effects. HC can be extracted from a variety of sources, during which acetic acid is used for the extraction of collagen type I from bovine, porcine, marine, chicken, and fish cartilage. An enzymatic treatment combined with an acidic treatment has shown more efficient extraction results. Because of its properties, it is frequently employed in the food industry since it improves sensorial qualities, as well as in the cosmetic industry as a functional component in face and body cream because of its moisturizing properties. It is also used in the pharmaceutical development of antioxidant supplements often combined with hyaluronic acid and vitamin C. HC has an excellent therapeutic effect on osteoporosis and osteoarthritis, where a daily dose of 12 g enhances pain symptoms and contributes to bone health. It also increases mineral density and protects articular cartilage. This review presents the structure and properties of hydrolyzed collagen, which mainly consists of the amino acids glycine, proline and hydroxyproline in a triple helix, its extraction process and its sources, as well as its applications. In particular, the creation of Enzymatic Membrane Reactor allows the production of HC with different molecular weight distributions, allowing wider application.

Soft Deposition of Organic Molecules Based on Cluster-Induced Desorption for the Investigation of On-Surface and Surface-Mediated Reactions

Desorption/ionization induced by neutral clusters (DINeC) was employed for the soft transfer of organic and biomolecules, such as porphyrins and peptides, from a bulk sample onto any substrate of choice. Qualitative analysis of the deposition technique was performed by means of mass spectrometry, demonstrating that the deposited molecules remained intact due to the soft nature of the transfer process. Deposition rates were studied quantitatively using a quartz crystal microbalance; layers of intact biomolecules ranging from the submonolayer regime up to a few monolayers in thickness were realized. Mixed layers of molecules were deposited when two different sources of molecules were employed. The samples which were prepared based on this soft deposition method were used for the investigation of reactions of the deposited molecules with either coadsorbates on the surface or the surface itself. Examples include adduct formation of peptides with alkali metals on SiO2, the oxidation of peptides exposed to oxygen, as well as the metallization of porphyrins in interaction with the substrate.

Substrate Scope for Human Histone Lysine Acetyltransferase KAT8

Biomedically important histone lysine acetyltransferase KAT8 catalyses the acetyl coenzyme A-dependent acetylation of lysine on histone and other proteins. Here, we explore the ability of human KAT8 to catalyse the acetylation of histone H4 peptides possessing lysine and its analogues at position 16 (H4K16). Our synthetic and enzymatic studies on chemically and structurally diverse lysine mimics demonstrate that KAT8 also has a capacity to acetylate selected lysine analogues that possess subtle changes on the side chain and main chain. Overall, this work highlights that KAT8 has a broader substrate scope beyond natural lysine, and contributes to the design of new chemical probes targeting KAT8 and other members of the histone lysine acetyltransferase (KAT) family.

Hydrolyzed Collagen-Sources and Applications

Hydrolyzed collagen (HC) is a group of peptides with low molecular weight (3-6 KDa) that can be obtained by enzymatic action in acid or alkaline media at a specific incubation temperature. HC can be extracted from different sources such as bovine or porcine. These sources have presented health limitations in the last years. Recently research has shown good properties of the HC found in skin, scale, and bones from marine sources. Type and source of extraction are the main factors that affect HC properties, such as molecular weight of the peptide chain, solubility, and functional activity. HC is widely used in several industries including food, pharmaceutical, cosmetic, biomedical, and leather industries. The present review presents the different types of HC, sources of extraction, and their applications as a biomaterial.

Loss of water from protonated polyglycines: interconversion and dissociation of the product imidazolone ions

Imidazolones formed from polyglycines are located at the centre of the peptide backbone and dissociate more easily than interconvert.

Efficient Esterification of Oxidized l-Glutathione and Other Small Peptides

Oxidized l-glutathione was esterified to the tetra methyl ester using thionyl chloride in methanol solvent. Other alcohols were tested and the reaction progress was monitored via ESI-MS. This procedure proved to be compatible with other small peptides not containing serine and cysteine residues. In contrast to previously reported methods this procedure provided convenient access to esterified peptides requiring no purification, extended reaction times, or complicated reaction setups.

A density functional theory (DFT) study on gas-phase proton transfer reactions of derivatized and underivatized peptide ions generated by matrix-assisted laser desorption ionization

In this study, classic molecular dynamics (MD) simulations followed by density functional theory (DFT) calculations are employed to calculate the proton transfer reaction enthalpy shifts for native and derivatized peptide ions in the MALDI plume. First, absolute protonation and deprotonation enthalpies are calculated for native peptides (RPPGF and AFLDASR), the corresponding hexyl esters and three common matrices alpha-cyano-4-hydroxycinnamic acid (4HCCA), 2,5-dihydroxybenzoic acid (DHB), and 6 aza-2-thiothymine (ATT). From the proton exchange reaction calculations, protonation and deprotonation of the neutral peptides are thermodynamically favorable in the gas phase as long as the corresponding protonated/deprotonated matrix ions are present in the plume. Moreover, the gain in proton affinity shown by the ester ions suggests that the increase in ion yield is likely to be related to an easier proton transfer from the matrix to the peptide.

Evaluating reproducibility and similarity of mass and intensity data in complex spectra--applications to tubulin

We present a data processing approach based on the spectral dot product for evaluating spectral similarity and reproducibility. The method introduces 95% confidence intervals on the spectral dot product to evaluate the strength of spectral correlation; it is the only calculation described to date that accounts for both the non-normal sampling distribution of the dot product and the number of peaks the spectra have in common. These measures of spectral similarity allow for the recursive generation of a consensus spectrum, which incorporates the most consistent features from statistically similar replicate spectra. Taking the spectral dot product and 95% confidence intervals between consensus spectra from different samples yields the similarity between these samples. Applying the data analysis scheme to replicates of brain tubulin CNBr peptides enables a robust comparison of tubulin isotype expression and post-translational modification patterns in rat and cow brains.

Development of novel guanidino-labelling derivatisation (GLaD) reagents for liquid chromatography/matrix-assisted laser desorption/ionisation analysis

A new generation of guanidino-labelling (GLaD) reagents were developed for quantitative proteomics using offline microcapillary liquid chromatography (LC) matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS). In order to reduce the unwanted overlapping between the isotopic envelopes of the two differentially labelled peptide ions, a novel synthetic route was described for production of both (13)C- and (15)N-containing isotopomers of N,O-dimethylisourea. The use of these types of isotopes has no deleterious effect on the retention times of both differentially labelled peptides during offline microbore reversed-phase LC. In addition, the possibility to incorporate a mass difference of 4 Da can be exploited during post-source decay analysis to generate product ion spectra in which fragment ions containing the modifications appear as doublets in the corresponding product ion spectra, thus facilitating identification of the C-terminal fragment ions.

Ion formation mechanisms in UV-MALDI

Matrix Assisted Laser Desorption/Ionization (MALDI) is a very widely used analytical method, but has been developed in a highly empirical manner. Deeper understanding of ionization mechanisms could help to design better methods and improve interpretation of mass spectra. This review summarizes current mechanistic thinking, with emphasis on the most common MALDI variant using ultraviolet laser excitation. A two-step framework is gaining acceptance as a useful model for many MALDI experiments. The steps are primary ionization during or shortly after the laser pulse, followed by secondary reactions in the expanding plume of desorbed material. Primary ionization in UV-MALDI remains somewhat controversial, the two main approaches are the cluster and pooling/photoionization models. Secondary events are less contentious, ion-molecule reaction thermodynamics and kinetics are often invoked, but details differ. To the extent that local thermal equilibrium is approached in the plume, the mass spectra may be straightforwardly interpreted in terms of charge transfer thermodynamics.