O-Sulfo-L-serine

We present the results of direct dynamics simulations and DFT calculations aimed at elucidating the effect of O-sulfonation on the collision-induced dissociation for serine. Toward this end, direct dynamics simulations of both serine and sulfoserine were performed at multiple collision energies and theoretical mass spectra obtained. Comparisons to experimental results are favorable for both systems. Peaks related to the sulfo group are identified and the reaction dynamics explored. In particular, three significant peaks (m/z 106, 88, and 81) seen in the theoretical mass spectrum directly related to the sulfo group are analyzed as well as major peaks shared by both systems. Our analysis shows that the m/z 106 peaks result from intramolecular rearrangements, intermolecular proton transfer among complexes composed of initial fragmentation products, and at high energy side-chain fragmentation. The m/z 88 peak was found to contain multiple constitutional isomers, including a previously unconsidered, low energy structure. It was also observed that the RM1 semiempirical method was not able to obtain all of the major peaks seen in experimens for sulfoserine. In contrast, PM6 did obtain all major experimental peaks.

Nattokinase (NK) is a serine protease extracted from a traditional Japanese food called natto. Due to its strong fibrinolytic and thrombolytic activity, NK is regarded as a valuable dietary supplement or nutraceutical for the oral thrombolytic therapy. In addition, NK has been investigated for some other medical applications including treatment of hypertension, Alzheimer's disease, and vitreoretinal disorders. The most widely used clinical anticoagulants are heparin and low molecular weight heparins. The interactions between heparin and proteins modulate diverse patho-physiological processes and heparin modifies the activity of serine proteases. Indeed, heparin plays important roles in almost all of NK's potential therapeutically applications. The current report relies on surface plasmon resonance spectroscopy to examine NK interacting with heparin as well as other glycosaminoglycans (GAGs). These studies showed that NK is a heparin binding protein with an affinity of ~250 nM. Examination with differently sized heparin oligosaccharides indicated that the interaction between NK and heparin is chain-length dependent and the minimum size for heparin binding is a hexasaccharide. Studies using chemically modified heparin showed the 6-O-sulfo as well as the N-sulfo groups but not the 2-O-sulfo groups within heparin, are essential for heparin's interaction with NK. Other GAGs (including HS, DS, and CSE) displayed modest binding affinity to NK. NK also interfered with other heparin-protein interactions, including heparin's interaction with antithrombin and fibroblast growth factors.

The structure of an intact glycosaminoglycan (GAG) chain of the bikunin proteoglycan (PG) was analyzed using a combined top-down and bottom-up sequencing strategy. PGs are proteins with one or more linear, high-molecular weight, sulfated GAG polysaccharides O-linked to serine or threonine residues. GAGs are often responsible for the biological functions of PGs, and subtle variations in the GAG structure have pronounced physiological effects. Bikunin is a serine protease inhibitor found in human amniotic fluid, plasma, and urine. Bikunin is posttranslationally modified with a chondroitin sulfate (CS) chain, O-linked to a serine residue of the core protein. Recent studies have shown that the CS chain of bikunin plays an important role in the physiological and pathological functions of this PG. While no PG or GAG has yet been sequenced, bikunin, the least complex PG, offers a compelling target. Electrospray ionization Fourier transform-ion cyclotron resonance mass spectrometry (ESI FTICR-MS) permitted the identification of several major components in the GAG mixture having molecular masses in a range of 5505-7102 Da. This is the first report of a mass spectrum of an intact GAG component of a PG. FTICR-MS analysis of a size-uniform fraction of bikunin GAG mixture obtained by preparative polyacrylamide gel electrophoresis, allowed the determination of chain length and number of sulfo groups in the intact GAGs.