mnn1

MNN1 is a gene found in several fungi, most notably the budding yeast Saccharomyces cerevisiae, where it encodes an alpha-1,3-mannosyltransferase involved in the elongation of the outer chain of N- and O-linked glycans. The name reflects its role in mannosylation during glycoprotein processing in the secretory pathway. MNN1 and its homologs are part of a broader family of Golgi-resident glycosyltransferases that shape the structure of fungal cell wall glycoproteins.

The enzyme expressed by MNN1 functions in the Golgi lumen, where it transfers mannose residues from GDP-mannose onto existing glycan acceptors to form alpha-1,3-linked branches. This activity contributes to the formation of extended mannan outer chains on glycoproteins, influencing the glycosylation pattern that emerges on the cell surface.

Genetic and cellular context shows that MNN1 encodes a type II membrane protein with a cytosolic N-terminus, a single transmembrane domain, and a luminal catalytic region. In yeast models, disruption of MNN1 often results in shortened outer chain mannans and altered cell wall properties, reflecting changes in glycoprotein maturation and cell surface architecture. Orthologous genes are present in other fungal species, where they similarly participate in glycan modification and cell wall structure.

Significance of MNN1 lies in its contribution to understanding fungal glycosylation pathways, cell wall integrity, and the interplay between glycan structure and protein function. Research on MNN1 and related enzymes informs studies of yeast biology, glycoprotein processing, and, in pathogenic fungi, potential impacts on host interactions and virulence.