Characterization of haemagglutinin-esterase protein (HE) of murine corona virus DVIM by monoclonal antibodies

Abstract

We analyzed the characteristics of seven monoclonal antibodies (mAbs) raised against purified HE (hemagglutinin-esterase) glycoprotein of the murine coronavirus DVIM (diarrhea virus of infant mice). Immunocrossreaction of these mAbs with JHM and/or MHV-S suggest that antigenic epitopes of HE of DVIM are similar to those of JHM and/or MHV-S. Four mAbs (1b4, 3a28, 4c19, 10b7), designated as group A mAbs, strongly inhibited both HA and AE activities. On the other hand, three mAbs (5a3, 6a6, 13a4), referred to as group B, had a comparatively weak HA inhibition activity. These results indicate that the antigenic epitopes of this glycoprotein can be classified into at least two groups and that the functional sites of HA and AE activities are similar but not identical. Neutralizing activity was shown in group A mAbs exclusively, suggesting that the ratio of HA and/or AE activities may play important roles in the cell fusion activity of DVIM-infected cells.

Structure, function and evolution of the hemagglutinin-esterase proteins of corona- and toroviruses

“…There is ample evidence in support: (i) mammalian cells, heterologously expressing HEs of BCoV, MHV-JHM, or BToV HE, display hemadsorption [74,76]; L.A.H.M. Cornelissen and R.J. de Groot, unpublished observations), (ii) the HE proteins of BCoV, PHEV and MHV-DVIM, purified from virions by detergent extraction and sucrose-gradient centrifugation, agglutinate rat and mouse erythrocytes in a Neu5,9Ac 2dependent fashion [92,93,102,103], (iii) the hemagglutinating activity of BCoV and MHV-DVIM can be inhibited by HE-specific monoclonal antibodies [67,[104][105][106], (iv) bromelain-treatment of BCoV and HCoV-OC43 virions results in degradation of the S protein, but leaves both the HE and the hemagglutinating activity unaffected [69,70].…”

“…The single cysteine residue Cys 6 at the N-terminus of HEF 1 , which forms an intermolecular disulfide bond with Cys 137 of HEF 2 [31], is absent in nidovirus HE proteins. In coronavirus HEs, bonds equivalent to those between HEF Cys 106 and Cys 151 (C3-C5; E domain) and between Cys 196 and Cys 238 (C7-C10; R domain) are lacking, whereas in torovirus HEs, the C7-C10 bond apparently has been replaced by a disulfide bond between C10 and a new cysteine residue, C9a. In turn, a surface loop, which in HEF 1 walls the esterase substrate binding pocket (residues 61-77), is closed by a disulfide bond (C1-C2) in the nidoviral HEs, but not in HEF 1 (Figure 6) [31].…”