Journal of Virology, September 1998, p. 7091-7098, Vol. 72, No. 9
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Department of
Microbiology1 and
Center for Oral Health
Research,
Received 26 March 1998/Accepted 3 June 1998
Glycoprotein D (gD) of herpes simplex virus (HSV) is essential for
virus entry and has four functional regions (I to IV) important for
this process. We previously showed that a truncated form of a
functional region IV variant, gD1(
290-299t), had an enhanced ability to block virus entry and to bind to the herpesvirus entry mediator (HveAt; formerly HVEMt), a cellular receptor for HSV. To
explore this phenotype further, we examined other forms of gD,
especially ones with mutations in region IV. Variant proteins with
deletions of amino acids between 277 and 300 (region IV), as well as
truncated forms lacking C-terminal residues up to amino acid 275 of gD,
were able to block HSV entry into Vero cells 1 to 2 logs better than
wild-type gD1(306t). In contrast, gD truncated at residue 234 did
not block virus entry into Vero cells. Using optical biosensor
technology, we recently showed that gD1(
290-299t) had a
100-fold-higher affinity for HveAt than gD1(306t) (3.3 × 10
8 M versus 3.2 × 10
6 M). Here we
found that the affinities of other region IV variants for HveAt were
similar to that of gD1(
290-299t). Thus, the affinity data follow
the same hierarchy as the blocking data. In each case, the higher
affinity was due primarily to a faster kon
rather than to a slower koff. Therefore, once
the gDt-HveAt complex formed, its stability was unaffected by mutations
in or near region IV. gD truncated at residue 234 bound to HveAt with a
lower affinity (2.0 × 10
5 M) than did gD1(306t)
due to a more rapid koff. These data suggest that residues between 234 and 275 are important for maintaining stability of the gDt-HveAt complex and that functional region IV is
important for modulating the binding of gD to HveA. The binding
properties of any gD1(234t)-receptor complex could account for the
inability of this form of gDt to block HSV infection.
*
Corresponding author. Mailing address: Department of
Microbiology, School of Dental Medicine, University of Pennsylvania, 4010 Locust St., Philadelphia, PA 19104-6002. Phone: (215) 898-6553. Fax: (215) 898-8385. E-mail:
ahrux{at}biochem.dental.upenn.edu.
Present address: Institute for Biochemistry, Swiss Federal
Institute of Technology, 8092 Zurich, Switzerland.
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