TABLE 1.

Summary of mutant envelope glycoproteins and viruses

Envelope glycoprotein	Cell-cell fusion activitya	Tm of gp41 six-helix bundle (°C)a,b	Viral infectivityc	gp120 per viriond (arbitrary units)
Wild type	+++	70	4,500	0.15
L556A	±	64	330	0.13
L565A	±	50	120	0.20
V570A	±	56	15	0.16
Q551A	+++	74	2,500	0.16
Q563A	+++	68	21,000	0.27

^aThe results are from reference 31.

^bThe melting temperature (T_m) of the gp41 six-helix bundle was determined in the N34(L6)C28 model (29).

^cp24 was determined by antigen capture enzyme-linked immunosorbent assay (Beckman Coulter, Inc.). Nominal viral infectivity (number of foci per nanogram of p24) was calculated by using a dilution of virus that produced 100 foci in a 96-well U87-CD4-CXCR4 cell microculture assay.

^dThe relative amount of gp120 per virion was estimated by Western blot analysis of centrifugally purified virions (51). gp120 was determined with the deglycosylated 55-kDa polypeptide of gp120 (31) and the anti-gp120 MAb Chessie 12 (1). Virion core protein p17 was assessed using immunoglobulin from HIV-infected persons (HIVIG). Antibody binding was visualized by ECL-Plus (Amersham Pharmacia Biotech), and fluorescence was quantitated using a Fuji FLA-3000G analyzer. The ratio of fluorescence intensities is shown.