Arabinosyltransferase (None established; sometimes abbreviated as "Aft" for specific isoforms (e.g., AftA, AftC) in mycobacteria)

Molecular Classification

Enzyme, Glycosyltransferase, Membrane-bound glycosyltransferase, Carbohydrate-active enzyme (CAZy GT family)

Other Names

Arabinofuranosyltransferase (more precise for mycobacterial enzymes), AftA, AftB, AftC (isoforms in mycobacteria), ARAD proteins (in plants)

Disease Roles

Infection (Mycobacterium tuberculosis, leprosy—critical for pathogen survival and virulence)Disease resistance in plants via modification of secondary metabolites like saponins

Arabinosyltransferase Overview

Arabinosyltransferases are membrane-bound glycosyltransferase enzymes that catalyze the transfer of arabinose residues, typically from decaprenylphosphoryl-arabinose donors onto acceptor molecules such as galactan chains. In mycobacteria, they are essential components responsible for building complex polysaccharides like arabinogalactan and lipoarabinomannan, which form critical parts of the unique mycobacterial cell envelope—a structure vital both for bacterial viability and pathogenicity. The best-characterized members include several isoforms such as AftA, which initiates attachment of the first arabinan residue during polymer assembly; other isoforms introduce branch points or extend chains further along biosynthetic pathways. These enzymes are also found across plant species where they participate in modifying secondary metabolites important for disease resistance. In medicine, particularly infectious disease therapeutics against tuberculosis, these enzymes represent validated drug targets—most notably inhibited by ethambutol. Inhibition disrupts cell wall formation leading to bacteriostasis or death. Technical challenges remain regarding assay development due to their membrane association and substrate requirements but ongoing structural studies continue to inform new inhibitor design strategies.

Mechanism of Action

Ethambutol inhibits the transfer of arabinose residues during the polymerization of arabinogalactan/lipoarabinomannan by binding to membrane-bound arabinosyltransferases, thereby disrupting cell wall synthesis and leading to bacterial death or stasis

Biological Functions

Cell wall biosynthesis (notably arabinogalactan and lipoarabinomannan synthesis in mycobacteria)

Polymerization of arabinan domains onto galactan chains

Glycosylation of plant natural products such as saponins and flavonoids

Disease Associations

Infection (Mycobacterium tuberculosis, leprosy—critical for pathogen survival and virulence)

Disease resistance in plants via modification of secondary metabolites like saponins

Safety Considerations

Difficulty isolating these membrane proteins for study or drug screening due to their hydrophobic nature and requirement for lipid environments.
Limited availability/commercial production challenges with natural substrates required for enzymatic assays.
Resistance development is a concern with drugs targeting these enzymes.

Interacting Drugs

Ethambutol (EMB), a first-line antitubercular drug that inhibits arabinosyltransferases involved in cell wall assembly

Associated Biomarkers

Biomarker
No widely used clinical biomarkers specifically for patient selection or efficacy monitoring related directly to this target. However, mutations conferring ethambutol resistance can be monitored genetically.