Catalyzes the final step in the biosynthesis of the membrane lipid glucosylceramide (GluCer), the transfer of glucose to ceramide. Glucosylceramides play important roles in growth, differentiation and pathogenicity. an N-acylsphing-4-enine + UDP-alpha-D-glucose = a beta-D-glucosyl-(1<->1')-N-acylsphing-4-enine + H(+) + UDP Lipid metabolism; sphingolipid metabolism. The D1, D2, D3, (Q/R)XXRW motif is a critical part of the GCS active site, involved in catalysis and UDP-sugar binding. Results in complete loss of glucosylceramides (GluCers) in mutant cells (PubMed:11443131). Has a decreased hyphal growth rate and increased susceptibility to SDS and fluconazole, suggesting defects in the cell membrane structure (PubMed:20019081). Shows increased resistance to plant defensin RsAFP2, and to heliomicin, a defensin-like peptide from the insect Heliothis virescens (PubMed:14604982). Belongs to the glycosyltransferase 2 family.