PMT4

PMT4 is a gene and protein name used for a member of the protein O-mannosyltransferase (PMT) family in eukaryotes. In many yeasts and other organisms, PMT4 encodes a multi-pass transmembrane enzyme that resides in the endoplasmic reticulum and participates in the initiation of O-linked glycosylation by transferring mannose from dolichyl phosphate mannose to serine or threonine residues on target proteins.

The PMT family comprises several paralogs, often labeled PMT1, PMT2, PMT3, PMT4, and so on. PMT4 typically functions alongside other PMT proteins, contributing to substrate selection and the overall efficiency of O-mannosylation. While PMT4 is not usually essential for viability, its activity supports proper glycosylation of secreted and membrane proteins, which in turn can influence protein folding, stability, and trafficking.

Phenotypically, loss or impairment of PMT4 can lead to reduced levels of O-mannosylation and increased sensitivity to cell wall–perturbing agents or environmental stresses. Because of redundancy among PMT paralogs, single-gene disruptions often yield milder phenotypes, whereas combined mutations or stress conditions can reveal more pronounced defects related to cell wall integrity and glycoprotein function.

In broader terms, PMT4 or its orthologs are found across eukaryotes, where they generally participate in O-mannosylation of extracellular and cell-surface proteins. In pathogenic fungi, PMT4 homologs can influence virulence traits such as cell wall composition and surface protein function. In plants and animals, PMT family members contribute to development and stress responses through their role in glycosylation.

See also: protein O-mannosyltransferase family, O-mannosylation, PMT1–PMT6, cell wall integrity pathway.