STRUCTURAL STUDIES OF AN HRV14:HIV-1 V3 LOOP CHIMERA THAT INDUCES NEUTRALIZING ANTIBODIES AGAINST HIV-1. Edward Arnold, Dawn A. Resnick, Jianping Ding, Sheila C. Geisler, Greg Kamer, and Gail Ferstandig Arnold, CABM and Rutgers University Chemistry Department, 679 Hoes Lane, Piscataway, NJ 08854

Human rhinovirus 14 (HRV14) has been engineered for use as a live-virus vaccine against human immunodeficiency virus (HIV-1). An HRV14:HIV-1 chimeric virus, designated DN-6, contains an immunogenic region from the V3 loop of the gp120 surface glycoprotein of HIV-1 transplanted into the neutralizing immunogenic site II of HRV14. DN-6 is strongly neutralized by anti-HIV-1 antibody preparations and elicits the production of antisera that potently neutralize HIV-1 in cell culture (Resnick et al., 1995). The crystal structure of DN-6 will reveal the conformation of a V3 loop epitope that is able to elicit a neutralizing response against HIV-1.

Crystals of DN-6 were obtained that diffract X-rays to 2.8 Å resolution. A native dataset measured at CHESS from cooled crystals is 44.8% complete to 3.5 Å resolution (238,364 independent reflections, R_merge=11.7%) and from a flash-frozen crystal is 61.4% complete to 3.5 Å resolution (322,463 independent reflections, R_merge=14.7%). The crystal symmetry and unit cell dimensions are similar to those of the orthorhombic crystal forms of HRV14 (Erickson et al., 1983) and poliovirus type 1 Mahoney (Hogle et al., 1985). Surprisingly, although the cell dimensions are very similar, the packing is different from that of the poliovirus 1 Mahoney crystals and the space group is P22₁2₁ instead of P2₁2₁2. The reflections were indexed accordingly for the standard space group choice P2₁2₁2 with a=378.4, b=354.7, and c=317.7 Å.

Rotation and translation functions indicated a particle rotation of 93.0deg. (cooled) or 94.2deg. (frozen) around the z axis relative to a standard icosahedral orientation and the particle center position to be close to z=0.25. Rigid body refinement using the HRV14 native coordinates (Rossmann et al., 1985; Arnold & Rossmann, 1988) yielded an R-factor of 0.34 for 15-3.5 Å resolution for the cooled dataset. Phase improvement by 30-fold noncrystallographic symmetry averaging is underway. Electron density is well ordered for the majority of the protein shell. We are in the process of interpreting the density in the chimeric region in terms of the structure of the transplanted HIV-1 V3 loop immunogen.