"Specific enzymatic cleavages in vivo yield mature proteins. Envelope glycoproteins are synthesized as a inactive precursor that is heavily N-glycosylated and processed likely by host cell furin in the Golgi to yield the mature SU and TM proteins. The cleavage site between SU and TM requires the minimal sequence [KR]-X-[KR]-R. About 2 of the 9 disulfide bonds of gp41 are reduced by P4HB/PDI, following binding to CD4 receptor."xsd:string