Chemo-enzymatic approaches to the biosynthesis of sialylated materials — ASN Events
  1. Schedule
  2. Session 7: Poster Session B - Including Happy Hour & Trade Display
  3. Chemo-enzymatic approaches to the biosynthesis of sialylated materials

Chemo-enzymatic approaches to the biosynthesis of sialylated materials (#228)

Andrew Muscroft-Taylor 1 , Simona Seizova 2 , Huisman Frances 3 , Renwick Dobson 2
  1. Protein Science and Engineering, Callaghan Innovation, Christchurch, Canterbury, New Zealand
  2. School of Biological Sciences, University of Canterbury, Christchurch, Canterbury, New Zealand
  3. Department of Chemistry, University of Canterbury, Christchurch, Canterbury, New Zealand

Sialic acid is undoubtedly one of the most important carbohydrates in biology. It is the terminal sugar unit found on most mammalian glycoconjugates, including glycoproteins and glycolipids attached to cell surfaces, and upon cytosolic or serum-located proteins and antibodies. Variations in sialic acid on cell surfaces can profoundly influence cell-cell and cell-pathogen interactions including inflammation, cell signalling, and may provide pre-cancer markers. Sialylation of cytosolic proteins influences their pharmacodynamic and pharmacokinetic properties including receptor binding, processing and rates of clearance with implications for natural and therapeutic species. Interestingly, many pathogenic organisms attempt to mimic sialyl-glycoconjugates to avoid host innate immunity responses.

Methods of preparing sialic acid-functionalised glycans and glycoproteins are chemically limited due to the difficulty of chemically synthesizing and then installing the sialic acid unit. Chemo-enzymatic approaches offer a solution to this difficulty.

Two types of enzymes catalyse the conversion of N-acetyl-glucosamine (GlcNAc) to N-acetyl-mannosamine (ManNAc) via epimerisation of the C2 N-acetyl-amine group, the first step within the sialic acid biosynthetic pathway. UDP-GlcNAc epimerase [E.C. 5.1.3.14] (UDP-AGE) widely distributed in mammals and bacteria supplies ManNAc via a high-energy irreversible reaction driven by hydrolysis of precursor substrate UDP-GlcNAc. N-Acetyl-D-glucosamine-epimerase [E.C. 5.1.3.8] (AGE) in contrast catalyses the reversible thermodynamic equilibration between GlcNAc and ManNAc and is believed to play a catabolic scavenger role in the sialic pathway. From a chemo-enzymatic perspective, the second of these enzymes is more suited for incorporation within a sequential enzymatic pathway.

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Few bacterial AGEs have been characterised, and the mechanism of epimerisation is not well understood. We report upon the biophysical characterisation of cyanobacterial AGEs from Anabaena sp. CH1 and Synechocystis sp. PCC 6803, two AGEs previously employed in a chemo-enzymatic context for sialic acid production. Both of these enzymes utilise ATP as non-consumed structural co-factor.

The Callaghan Innovation Protein Science and Engineering Team was established in 2012 and is based within the Biomolecular Interaction Centre (BIC) at the University of Canterbury, New Zealand. Currently, we are exploring industrially applicable enzymes and processes within the sialic acid biosynthetic pathway that will enable new or improved methods of preparing sialic acid functionalised molecules, materials and glycoproteins.