Binding a heparin derived disaccharide to defensin inspired peptides: insights to antimicrobial inhibition from gas-phase measurements

Soluble fusion expression, characterization and localization of human β-defensin 6

Human β‑defensin 6 (DEFB106) is an antimicrobial peptide expressed in the epididymis, testis and lung, which indicates that DEFB106 may be involved in innate immunity and fertility. However, as a β‑defensin, this protein has not been well characterized. Using an intein‑mediated fusion expression system, the recombinant DEFB106 was expressed and purified (yield, 3‑5 mg/l) under optimized conditions. The purified protein was characterized using mass spectrometry and circular dichroism spectroscopy. The measured molecular weight was consistent with its theoretical value and the predominant secondary structure was β‑sheet, the common structure of β‑defensin family members. The purified DEFB106 showed antimicrobial activity against not only Escherichia coli (E. coli) and Candida albicans (C. albicans) SC5314, but also Staphylococcus aureus (S. aureus) CMCC26003. Furthermore, it exhibited a high affinity for heparin and lipopolysaccharide. In addition, it was determined that native DEFB106 was located in the epididymis, bone marrow and skin. These observations may aid in the determination of the physiological and pathological functions of DEFB106.

Structural separations by ion mobility-MS for glycomics and glycoproteomics

This chapter describes the utility of ion mobility-mass spectrometry (IM-MS) for the detection and characterization of glycoproteins and associated glycoconjugates. IM-MS provides separations in two dimensions; one on the basis of molecular surface area or structure, and the other on molecular mass which creates the ability to differentiate biomolecular classes and isobaric species. When applied to the characterization of glycoproteins, IM-MS separates peptides from the associated glycans in the same digest without purification, and can also be used to separate different isomeric glycans which is a significant challenge in current glycomic studies. The chapter details the methodologies to use IM-MS for the study of glycans and glycoproteins for an audience ranging from new and potential practitioners to those already utilizing the technique.

Directing the biological activities of heparan sulfate oligosaccharides using a chemoenzymatic approach

Heparan sulfate (HS) and heparin are highly sulfated polysaccharides exhibiting essential physiological functions. The sulfation patterns determine the functional selectivity for HS and heparin. Chemical synthesis of HS, especially those larger than a hexasaccharide, remains challenging. Enzymatic synthesis of HS has recently gained momentum. Here we describe the divergent assembly of HS heptasaccharides and nonasaccharides from a common hexasaccharide precursor. The hexasaccharide precursor was synthesized via a chemical method. The subsequent elongation, sulfation and epimerization were completed by glycosyltransferases, HS sulfotransferases and epimerase. Using the synthesized heptasaccharides, we discovered that the iduronic acid is critical for binding to fibroblast growth factor-2. We also designed a synthetic path to prepare a nonasaccharide with an antithrombin-binding affinity of 3 nM. Our method demonstrated the feasibility of combining chemical and enzymatic synthesis to prepare structurally defined HS oligosaccharides with desired biological activities.

Ion mobility mass spectrometry for peptide analysis

The use of ion mobility mass spectrometry has grown rapidly over the last two decades. This powerful analytical platform now forms an attractive prospect for comprehensive analysis of many different molecular species, including chemically complex biological molecules. This paper describes the application of IM-MS to the study of peptides. We focus on three different ion mobility devices that are most frequently found in tandem with mass spectrometers. These are instruments using linear drift tubes (LDT), those using travelling wave ion guides (TWIGS) and those employing high field asymmetric ion mobility spectrometry (FAIMS). Each technique is described. Examples are given on the use of IM-MS for the determination of peptide structure, the study of peptides that form amyloid fibrils, and the study of complex peptide mixtures in proteomic investigations. We describe and comment on the methodologies used and the outlook for this developing analytical technique.

Interaction of human β-defensin 2 (HBD2) with glycosaminoglycans

Human β-defensin 2 (HBD2) is a member of the defensin family of antimicrobial peptides that plays important roles in the innate and adaptive immune system of both vertebrates and invertebrates. In addition to their direct bactericidal action, defensins are also involved in chemotaxis and Toll-like receptor activation. In analogy to chemokine/glycosaminoglycan (GAG) interactions, GAG-defensin complexes are likely to play an important role in chemotaxis and in presenting defensins to their receptors. Using a gel mobility shift assay, we found that HBD2 bound to a range of GAGs including heparin/heparan sulfate (HS), dermatan sulfate (DS), and chondroitin sulfate. We used NMR spectroscopy of (15)N-labeled HBD2 to map the binding sites for two GAG model compounds, a heparin/HS pentasaccharide (fondaparinux sodium; FX) and enzymatically prepared DS hexasaccharide (DSdp6). We identified a number of basic amino acids that form a common ligand binding site, which indicated that these interactions are predominantly electrostatic. The dissociation constant of the [DSdp6-HBD2] complex was determined by NMR spectroscopy to be 5 ± 5 μM. Binding of FX could not be quantified because of slow exchange on the NMR chemical shift time scale. FX was found to induce HBD2 dimerization as evidenced by the analysis of diffusion coefficients, (15)N relaxation, and nESI-MS measurements. The formation of FX-bridged HBD2 dimers exhibited features of a cooperative binding mechanism. In contrast, the complex with DSdp6 was found to be mostly monomeric.