Structural Insights into the Glycosylphosphatidylinositol Mannosyltransferase I Complex from Candida glabrata.

The global rise in resistance to first-line antifungal agents highlights the urgent need for new therapeutic strategies. Glycosylphosphatidylinositol (GPI)-anchored protein biosynthesis is an attractive target. The GPI mannosyltransferase I (GPI-MT-I), composed of Gpi14 and Pbn1, catalyzes the essential first mannose transfer from dolichol-phosphomannose (Dol-P-Man) to the GPI precursor. This initial mannosylation is critical for fungal cell wall integrity, yet the molecular basis of GPI-MT-I assembly and substrate recognition remains poorly understood. Here, we present the cryo-EM structure of Candida glabrata GPI-MT-I in complex with Dol-P-Man, revealing how Gpi14 and Pbn1 form a stable complex and engage the mannose donor. An AlphaFold3-predicted acceptor-bound model further defines the structural basis of acceptor substrate recognition and suggests a plausible catalytic mechanism. Comparison with structural homologs highlights a distinct mode of substrate engagement by GPI-MT-I. Together, these findings establish a mechanistic framework for GPI-MT-I function with broader implications for the GPI-MT family.