1,3-beta-D-glucan synthase (GS) (GS)

1,3-beta-D-glucan synthase (GS) is a multi-subunit enzyme complex essential for the synthesis of 1,3-beta-D-glucan, the primary structural polysaccharide of the fungal cell wall [4, 12]. It is located in the plasma membrane and consists of a catalytic subunit, typically encoded by the FKS1 or FKS2 genes, and a regulatory subunit, the Rho1 GTPase [3, 12]. The enzyme catalyzes the transfer of glucose from UDP-glucose to a growing glucan chain, which is then extruded into the periplasmic space to provide mechanical strength and osmotic protection to the fungal cell [7, 13]. Because this enzyme is absent in mammalian cells, it serves as a highly selective target for antifungal therapy [1, 12]. Drugs such as echinocandins (e.g., caspofungin, micafungin) and triterpenoids (e.g., ibrexafungerp) inhibit this enzyme non-competitively, leading to cell wall depletion, osmotic instability, and eventual cell lysis [5, 15]. Clinical resistance to these agents is primarily driven by point mutations in the "hotspot" regions of the FKS genes, which reduce the binding affinity of the drugs to the enzyme complex [3, 14]. While generally well-tolerated due to its fungal specificity, challenges include a limited spectrum of activity against certain fungi like Cryptococcus and the emergence of multi-drug resistant strains such as Candida auris [12, 14].

Other names

beta-1,3-glucan synthaseFungal beta-1,3-D-glucan synthaseCallose synthaseUDP-glucose:1,3-beta-D-glucan 3-beta-D-glucosyltransferaseFKS1FKS2GS-IIParamylon synthetase

Non-competitive inhibition of the 1,3-beta-D-glucan synthase enzyme complex, specifically by binding to the Fks catalytic subunits, which prevents the polymerization of UDP-glucose into 1,3-beta-D-glucan and leads to fungal cell wall depletion and osmotic lysis.