Disintegrin-like domain of glycoprotein B regulates Kaposi's sarcoma-associated herpesvirus infection of cells

Kaposi's sarcoma-associated herpesvirus (KSHV) glycoprotein B (gB) is a lytic structural protein expressed on the envelope of mature virions and on the membrane of cells supporting lytic infection. In addition to this viral glycoprotein's interaction with integrins via its RGD (Arg-Gly-Asp) motif, KSHV gB possesses a disintegrin-like domain (DLD), which binds integrins as well. Prior to this study, there has been minimal research involving the less common integrin-binding motif, DLD, of gB as it pertains to herpesvirus infection. By using phage display peptide library screening and molecular biology techniques, the DLD of KSHV gB was shown to interact specifically with non-RGD binding alpha 9 beta 1 integrins. Similarly, monitoring wild-type infection confirmed alpha 9 beta 1 :DLD interactions to be critical to successful KSHV infection of human foreskin fibroblast (HFF) cells and human dermal microvascular endothelial cells (HMVEC-d) compared with 293 cells. To further demonstrate the importance of the DLD of gB in KSHV infection, two recombinant virus constructs were generated using a bacterial artificial chromosome (BAG) system harbouring the KSHV genome (BAC36): BAC36AD-KSHV (lacking a functionally intact DLD of gB and containing an introduced tetracycline cassette) and BAC36.T-KSHV (containing an intact DLD sequence and an introduced tetracycline cassette). Accordingly, BAC36AD-KSHV presented significantly lower infection rates in HFF and HMVEC-d cells compared with the comparable infection rates achieved by wild-type BAC36-KSHV and BAC36.T-KSHV. Thus, the present report has delineated a critical role for the DLD of gB in KSHV infection, which may lead to a broader knowledge regarding the sophisticated mechanisms utilized by virus-encoded structural proteins in KSHV entry and infection.