Once it binds to the specific cell receptor, it changes shape, allowing the virus to enter.
It starts as a precursor protein, which is glycosylated in the Golgi apparatus. Finally, it is cleaved by a cellular furin protease into the mature SU (roughly 70 kDa) and TM (Transmembrane) subunits.
SU (Surface) is a glycoprotein that mediates viral adsorption by binding to specific receptors on a cell surface. Think of it as the virus's "lock-picking" tool.
Based on the search results, "maturesu s a" likely refers to the of a retrovirus. This is a protein that plays a key role in how viruses bind to cell receptors, essentially acting as the key that unlocks the cell.