TABLE 2.

Fusion activity and cell surface expression of leucine zipper mutant S glycoproteins

Name	Substitutiona	Fusion activityb	Oligomerizationc	Endo H resistanced	Surface expressione
Wild type	LLLILL	100 ± 19	+	+	100 ± 16
L1217A	ALLILL	91 ± 15	ND	+	ND
L1224A	LALILL	81 ± 12	ND	+	ND
L1231A	LLAILL	89 ± 17	ND	+	ND
I1238A	LLLALL	84 ± 9	ND	+	ND
L1245A	LLLIAL	87 ± 16	ND	+	ND
L1252A	LLLILA	96 ± 11	ND	+	ND
L1217A-L1224A	AALILL	64 ± 11	+	+	94 ± 12
L1224A-L1231A	LAAILL	8 ± 3	−	+	78 ± 15
L1224A-I1238A	LALALL	19 ± 5	−	+	75 ± 10
L1224A-L1245A	LALIAL	7 ± 3	−	+	83 ± 14
L1224A-I1252A	LALILA	81 ± 18	+	+	80 ± 13
I1231A-L1245A	LLAIAL	9 ± 2	−	+	73 ± 11
I1238A-L1252A	LLLALA	103 ± 21	+	+	69 ± 14

^aHeptadic leucine and isoleucine residues in the leucine zipper domain of MHV-A59 S protein are shown. Alanine substitutions are indicated for each leucine zipper mutant. 

^bReported as the percentage of the β-Gal to be activity produced in samples expressing wild-type S protein, which is considered to be 100% (see Materials and Methods). All data are averages from at least three experiments, each of which was performed in triplicate analysis. The standard deviations are also shown. 

^cOligomerization status as determined by sucrose gradient assay. +, oligomeric forms of S were detected; −, oligomeric forms of S were missing for the respective leucine zipper mutants. Representative oligomerization profiles are shown in Fig. 4. ND, not determined. 

^dGlycosylation status as determined by endo H resistance assay as shown in Fig. 3. +, S protein was endo H resistant. 

^eReported as the percentage of the mean fluorescence intensity values compared with those of samples expressing the wild-type S protein after subtracting background values obtained for mock-transfected samples. Experiments were repeated twice, with a standard deviation of less than 20%. ND, not determined.