Biochemical and structural analysis of isolated mature cores of human immunodeficiency virus type 1

Mature human immunodeficiency virus type 1 (HIV-1) particles contain a cone -shaped core structure consisting of the internal ribonucleoprotein complex encased in a proteinaceous shell derived from the viral capsid protein. Be cause of their very low stability after membrane removal, HIV-1 cores have not been purified in quantities sufficient for structural and biochemical a nalysis. Based on our in vitro assembly experiments, we have developed a no vel method far isolation of intact mature HIV-1 cores. Concentrated virus s uspensions were briefly treated with nonionic detergent and immediately cen trifuged in a microcentrifuge for short periods of time. The resuspended pe llet was subsequently analyzed by negative-stain and thin-section electron microscopy and by immunoelectron microscopy. Abundant cone-shaped cores as well as tubular and aberrant structures were observed. Stereo images showed that core structures preserved their three-dimensional architecture and ex hibited a regular substructure. Detailed analysis of 155 cores revealed an average length of ca. 103 nm, an average diameter at the base of ca. 52 nm, and an average angle of 21.3 degrees. There was significant variability in all parameters, indicating that HIV cores are not homogeneous. Immunoblot analysis of core preparations allowed semiquantitative estimation of the re lative amounts of viral and cellular proteins inside the HIV-1 tore, yieldi ng a model for the topology of various proteins inside the virion.