Glycosphingolipids: from metabolism to chemoenzymatic total synthesis

GSLs are the major glycolipids in vertebrates and mediate many key biological processes from intercellular recognition to cis regulation of signal transduction. The fast-expanding field of glycobiology has led to a growing demand for diverse and structurally defined GSLs, and enzymatic GSL synthesis is developing rapidly in accordance. This article provides an overview of natural GSL biosynthetic pathways and surveys the bacterial enzymes applied to GSL synthesis and recent progress in synthesis strategies. By correlating these three areas, this article aims to define the gaps between GSL biosynthesis and chemoenzymatic synthesis and evaluate the opportunities for harnessing natural forces to access GSLs efficiently.

Comparison of Hyaluronic Acid Biosynthetic Genes From Different Strains of Pasteurella multocida

Pasteurella multocida produces a capsule composed of different polysaccharides according to the capsular serotype (A, B, D, E, and F). Hyaluronic acid (HA) is a component of certain capsular types of this bacterium, especially capsular type A. Previously, 2 HA biosynthetic genes from a capsular type A strain were studied for the industrial-scale improvement of HA production. Molecular comparison of these genes across different capsular serotypes of P multocida has not been reported. This study aimed to compare 8 HA biosynthetic genes (pgi, pgm, galU, hyaC, glmS, glmM, glmU, and hyaD) of 22 P multocida strains (A:B:D:F = 6:6:6:4) with those of other organisms using sequence and structural bioinformatics analyses. These 8 genes showed a high level of within-species similarity (98%-99%) compared with other organisms. Only the last gene of 4 strains with capsular type F (HN07, PM70, HNF01, and HNF02) significantly differed from those of other strains (82%). Analysis of amino acid patterns together with phylogenetic results showed that the HA biosynthetic genes of the type A were closely related within the group. The genes in the capsular type F strain were notably similar to those of the capsular type A strain. Protein structural analysis supported structural similarities of the encoded enzymes between the strains of capsular types A, B, D, and F, except for the Pgm, GlmS, GlmU, and HyaD proteins. Our bioinformatics analytic workflow proposed that variations observed within these genes could be useful for genetic engineering–based improvement of hyaluronic acid–producing enzymes.

Key Factors for A One-Pot Enzyme Cascade Synthesis of High Molecular Weight Hyaluronic Acid

In the last decades, interest in medical or cosmetic applications of hyaluronic acid (HA) has increased. Size and dispersity are key characteristics of biological function. In contrast to extraction from animal tissue or bacterial fermentation, enzymatic in vitro synthesis is the choice to produce defined HA. Here we present a one-pot enzyme cascade with six enzymes for the synthesis of HA from the cheap monosaccharides glucuronic acid (GlcA) and N-acetylglucosamine (GlcNAc). The combination of two enzyme modules, providing the precursors UDP–GlcA and UDP–GlcNAc, respectively, with hyaluronan synthase from Pasteurella multocida (PmHAS), was optimized to meet the kinetic requirements of PmHAS for high HA productivity and molecular weight. The Mg²⁺ concentration and the pH value were found as key factors. The HA product can be tailored by different conditions: 25 mM Mg²⁺ and 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid (HEPES)-NaOH pH 8 result into an HA product with high M_w HA (1.55 MDa) and low dispersity (1.05). Whereas with 15 mM Mg²⁺ and HEPES–NaOH pH 8.5, we reached the highest HA concentration (2.7 g/L) with a yield of 86.3%. Our comprehensive data set lays the basis for larger scale enzymatic HA synthesis.

Biosynthesis of Hyaluronic acid polymer: Dissecting the role of sub structural elements of hyaluronan synthase

Hyaluronic acid (HA) based biomaterials have several biomedical applications. HA biosynthesis is catalysed by hyaluronan synthase (HAS). The unavailability of 3-D structure of HAS and gaps in molecular understanding of HA biosynthesis process pose challenges in rational engineering of HAS to control HA molecular weight and titer. Using in-silico approaches integrated with mutation studies, we define a dictionary of sub-structural elements (SSE) of the Class I Streptococcal HAS (SeHAS) to guide rational engineering. Our study identifies 9 SSE in HAS and elucidates their role in substrate and polymer binding and polymer biosynthesis. Molecular modelling and docking assessment indicate a single binding site for two UDP-substrates implying conformationally-driven alternating substrate specificities for this class of enzymes. This is the first report hypothesizing the involvement of sites from SSE5 in polymer binding. Mutation at these sites influence HA production, indicating a tight coupling of polymer binding and synthase functions. Mutation studies show dispensable role of Lys-139 in substrate binding and a key role of Gln-248 and Thr-283 in HA biosynthesis. Based on the functional architecture in SeHAS, we propose a plausible three-step polymer extension model from its reducing end. Together, these results open new avenues for rational engineering of Class I HAS to study and regulate its functional properties and enhanced understanding of glycosyltransferases and processive enzymes.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Directed Evolution of Hyaluronic Acid Synthase from Pasteurella multocida towards High-Molecular-Weight Hyaluronic Acid

Hyaluronic acid (HA), with diverse cosmetic and medical applications, is the natural glycosaminoglycan product of HA synthases. Although process and/or metabolic engineering are used for industrial HA production, the potential of protein engineering has barely been realised. Herein, knowledge-gaining directed evolution (KnowVolution) was employed to generate an HA synthase variant from Pasteurella multocida (pmHAS) with improved chain-length specificity and a twofold increase in mass-based turnover number. Seven improved pmHAS variants out of 1392 generated by error-prone PCR were identified; eight prospective positions were saturated and the most beneficial amino acid substitutions were recombined. After one round of KnowVolution, the longest HA polymer (<4.7 MDa), through an engineered pmHAS variant in a cell-free system, was synthesised. Computational studies showed that substitutions from the best variant (T40L, V59M and T104A) are distant from the glycosyltransferase sites and increase the flexibility of the N-terminal region of pmHAS. Taken together, these findings suggest that the N terminus may be involved in HA synthesis and demonstrate the potential of protein engineering towards improved HA synthase activity.

Biotechnological production of hyaluronic acid: a mini review

Hyaluronic acid (HA) is a polysaccharide found in the extracellular matrix of vertebrate epithelial, neural and connective tissues. Due to the high moisture retention, biocompatibility and viscoelasticity properties of this polymer, HA has become an important component of major pharmaceutical, biomedical and cosmetic products with high commercial value worldwide. Currently, large scale production of HA involves extraction from animal tissues as well as the use of bacterial expression systems in Streptococci. However, due to concerns over safety, alternative sources of HA have been pursued which include the use of endotoxin-free microorganisms such as Bacilli and Escherichia coli. In this review, we explore current knowledge of biosynthetic enzymes that produce HA, how these systems have been used commercially to produce HA and how the challenges of producing HA cheaply and safely are being addressed.