Liposomes for Improved Enzymatic Glycosylation of Lipid-Modified Lactose Enkephalin

The Lst Sialyltransferase of Neisseria gonorrhoeae Can Transfer Keto-Deoxyoctanoate as the Terminal Sugar of Lipooligosaccharide: a Glyco-Achilles Heel That Provides a New Strategy for Vaccines to Prevent Gonorrhea

The lipooligosaccharide (LOS) of Neisseria gonorrhoeae plays key roles in pathogenesis and is composed of multiple possible glycoforms. These glycoforms are generated by the process of phase variation and by differences in the glycosyltransferase gene content of particular strains. LOS glycoforms of N. gonorrhoeae can be terminated with an N-acetylneuraminic acid (Neu5Ac), which imparts resistance to the bactericidal activity of serum. However, N. gonorrhoeae cannot synthesize the CMP-Neu5Ac required for LOS biosynthesis and must acquire it from the host. In contrast, Neisseria meningitidis can synthesize endogenous CMP-Neu5Ac, the donor molecule for Neu5Ac, which is a component of some meningococcal capsule structures. Both species have an almost identical LOS sialyltransferase, Lst, that transfers Neu5Ac from CMP-Neu5Ac to the terminus of LOS. Lst is homologous to the LsgB sialyltransferase of nontypeable Haemophilus influenzae (NTHi). Studies in NTHi have demonstrated that LsgB can transfer keto-deoxyoctanoate (KDO) from CMP-KDO to the terminus of LOS in place of Neu5Ac. Here, we show that Lst can also transfer KDO to LOS in place of Neu5Ac in both N. gonorrhoeae and N. meningitidis Consistent with access to the pool of CMP-KDO in the cytoplasm, we present data indicating that Lst is localized in the cytoplasm. Lst has previously been reported to be localized on the outer membrane. We also demonstrate that KDO is expressed as a terminal LOS structure in vivo in samples from infected women and further show that the anti-KDO monoclonal antibody 6E4 can mediate opsonophagocytic killing of N. gonorrhoeae Taken together, these studies indicate that KDO expressed on gonococcal LOS represents a new antigen for the development of vaccines against gonorrhea.IMPORTANCE The emergence of multidrug-resistant N. gonorrhoeae strains that are resistant to available antimicrobials is a current health emergency, and no vaccine is available to prevent gonococcal infection. Lipooligosaccharide (LOS) is one of the major virulence factors of N. gonorrhoeae The sialic acid N-acetylneuraminic acid (Neu5Ac) is present as the terminal glycan on LOS in N. gonorrhoeae In this study, we made an unexpected discovery that KDO can be incorporated as the terminal glycan on LOS of N. gonorrhoeae by the alpha-2,3-sialyltransferase Lst. We showed that N. gonorrhoeae express KDO on LOS in vivo and that the KDO-specific monoclonal antibody 6E4 can direct opsonophagocytic killing of N. gonorrhoeae These data support further development of KDO-LOS structures as vaccine antigens for the prevention of infection by N. gonorrhoeae.

‘One-pot’ sequential enzymatic modification of synthetic glycolipids in vesicle membranes

To create vesicles with cell-targeting coatings, two soluble enzymes were used to directly glycosylate vesicle surfaces in a ‘one-pot’ procedure.

Glycosylation, an effective synthetic strategy to improve the bioavailability of therapeutic peptides

Glycosylation of peptides is a promising strategy for modulating the physicochemical properties of peptide drugs and for improving their absorption through biological membranes. This review highlights various methods for the synthesis of glycoconjugates and recent progress in the development of glycosylated peptide therapeutics. Furthermore, the impacts of glycosylation in overcoming the existing barriers that restrict oral and brain delivery of peptides are described herein.

A drug delivery strategy: binding enkephalin to asialoglycoprotein receptor by enzymatic galactosylation

Glycosylation of biopharmaceuticals can mediate cell specific delivery by targeting carbohydrate receptors. Additionally, glycosylation can improve the physico-chemical (drug-like) properties of peptide based drug candidates. The main purpose of this study was to examine if glycosylation of the peptide enkephalin could facilitate its binding to the carbohydrate receptor, asialoglycoprotein. Firstly, we described the one-pot enzymatic galactosylation of lactose modified enkephalin in the presence of uridine-5'-diphosphogalactose 4-epimerase and lipopolysaccharyl α-1,4-galactosyltransferase. Stability experiments using human plasma and Caco-2 cell homogenates showed that glycosylation considerably improved the stability of enkephalin (at least 60% remained stable after a 2 hr incubation at 37°C). In vitro permeability experiments using Caco-2 cells revealed that the permeability of mono- and trisaccharide conjugated enkephalins was 14 and 28 times higher, respectively, than that of enkephalin alone (Papp 3.1×10-8 cm/s). By the methods of surface plasmon resonance and molecular modeling, we demonstrated that the enzymatic glycosylation of enkephalin enabled binding the asialoglycoprotein receptor. The addition of a trisaccharide moiety to enkephalin improved the binding of enkephalin to the asialoglycoprotein receptor two fold (KD = 91 µM). The docking scores from molecular modeling showed that the binding modes and affinities of the glycosylated enkephalin derivatives to the asialoglycoprotein receptor complemented the results from the surface plasmon resonance experiments.

Sialylation of lactosyl lipids in membrane microdomains byT. cruzi trans-sialidase

SolubleT. cruzi trans-sialidase transformed a synthetic lactosyl glycolipid in microdomains more slowly than the same substrate dispersed across the bilayer surface, producing phospholipid vesicles with a Neu5Ac(α2-3)Gal(β1-4)Glc “glycocalyx”.