Incorporation of wild-type and C-terminally truncated human epidermal growth factor receptor into human immunodeficiency virus-like particles: Insight into the processes governing glycoprotein incorporation into retroviral particles

Previous results have indicated that incorporation of surface glycoprotein into retroviral particles is not a specific process and that many heterolog ous viral and cellular glycoproteins can be incorporated as long as they do not have long cytoplasmic e-terminal regions which were presumed to be ste rically inhibitory. In this study, this concept has been directly examined by analyzing the incorporation of the wild-type human epidermal growth fact or receptor (Wt-EGFR) and of a C-terminally truncated mutant of Wt-EGFR (Tr -EGFR) into human immunodeficiency virus (HIV)-like particles. Incorporatio n was directly analyzed at the protein level and by immunogold labelling of enriched HIV-like particles. In agreement with the above concept, Tr-EGFR, with only 7 C-terminal amino acids (aa), was efficiently incorporated into HIV-like particles. Incorporation of the Wt-EGFR species, with 542 C-termi nal cytoplasmic aa, was reduced by a factor of about 5 in comparison to tha t of the Tr-EGFR species. However, the Wt-EGFR species was still very signi ficantly present in the HIV-like particles. A series of control experiments verified that this represents genuine incorporation of Wt-EGFR into the me mbrane of HIV-like particles. These observations allow further speculation as to the processes governing glycoprotein incorporation into retroviral pa rticles and indicate that the internal virus structure of HIV (in particula r the matrix layer [MA]) can accommodate much larger heterologous cytoplasm ic domains in incorporated glycoproteins than previously assumed.