The env gene does not, in fact, code for gp120 and gp41, but for a precursor to both, gp160. During HIV reproduction, the host cell's own enzymes cleave gp160 into gp120 and gp41. See Replication cycle of HIV.
A polyclonal caprine antibody is in phase II human clinical trials that targets, among others sites, the GP41 transmembrane glycoprotein. This is a new class of treatment for HIV infection. The trials are being conducted for a patented biologic developed by Virionyx, a New Zealand Company.
Structure and Plasticity of the Human Immunodeficiency Virus gp41 Fusion Domain in Lipid Micelles and Bilayers
Aug 01, 2007; ABSTRACT A thorough understanding of the structure of fusion domains of enveloped viruses in changing lipid environments helps us...