Msb2

Msb2 is a gene encoding a mucin-like transmembrane glycoprotein found in the budding yeast Saccharomyces cerevisiae and in related fungi. The protein contains a large extracellular, heavily glycosylated domain, a single membrane-spanning segment, and a short cytoplasmic tail, attributes common to cell surface sensors.

It functions as part of the osmosensing branch of the High Osmolarity Glycerol (HOG) pathway. Along with the plasma membrane protein Sho1, Msb2 transduces osmotic-stress signals to the MAP kinase cascade, leading to activation of the MAPKK Pbs2 and the MAPK Hog1. Hog1 then directs transcriptional and metabolic responses that help the cell adapt to high osmolarity, including glycerol accumulation to restore turgor pressure.

Regulation and processing: The extracellular region can be proteolytically processed; this cleavage is implicated in signal generation; the protein is also subject to glycosylation which influences localization and stability at the cell surface.

Genetics and evolutionary note: Msb2 homologs are widespread in fungi; while specific roles vary, these mucin-like sensors are generally linked to environmental sensing and signal transduction at the cell surface.

See also: High Osmolarity Glycerol pathway, Sho1, Pbs2, Hog1.