Proteoglycans: Structures And Interactions

Lintelo

et al. 2005

125

169

Only a relatively few mutations in its spike protein allow the murine coronavirus to switch from a murinerestricted tropism to an extended host range by being passaged in vitro. One such virus that we studied had acquired two putative heparan sulfate-binding sites while preserving another site in the furin-cleavage motif. The adaptation of the virus through the use of heparan sulfate as an attachment/entry receptor was demonstrated by increased heparin binding as well as by inhibition of infection through treatment of cells and the virus with heparinase and heparin, respectively.Coronaviruses are enveloped, plus-stranded RNA viruses, which generally cause respiratory and/or intestinal infections, although some may spread systemically. They are pathogens of veterinary importance, often associated with great economic losses. Their relevance has increased considerably since the recent emergence of new human coronaviruses (HCoV), such as the severe acute respiratory syndrome coronavirus (SARSCoV). In general, coronaviruses have a limited host range and cause disease in a single or a few closely related host species. However, the emergence of SARS-CoV, which resulted from a zoonotic transmission event (19), demonstrates the need for a better understanding of coronavirus interspecies transmission.The interaction of the coronavirus spike (S) protein, a class I fusion protein (5), with its receptor is the major determinant for virus entry and host range restriction. While nonpermissive cell lines can be rendered susceptible by making them express the receptor (see references below), coronaviruses can also be retargeted to specific cells by exchanging the ectodomain of the S protein with that of another appropriate coronavirus, as was demonstrated for mouse hepatitis virus (MHV) (24) and feline infectious peritonitis virus (20). Receptors have so far been identified for the group 2 coronavirus MHV (murine carcinoembryonic antigen-related cell adhesion molecule 1 [CEACAM1]) (16, 38), for SARS-CoV (ACE2) (26), for the group 1 coronaviruses transmissible gastroenteritis virus and porcine respiratory coronavirus (porcine APN) (12, 13), for feline infectious peritonitis virus (feline APN) (36), for HCoV-229E (human APN) (40), and for HCoV-NL63 (ACE2) (21).The S protein is synthesized as a heavily glycosylated polypeptide, which oligomerizes in the endoplasmic reticulum to form trimers (14, 27). As a late maturation step during its transport to the cell surface, cleavage of the MHV S protein into an amino-terminal S1 and a carboxy-terminal S2 domain can occur. A basic amino acid sequence resembling the furin consensus sequence motif occurs approximately in the middle of the protein and was shown to be the target of a furin-like enzyme in the case of MHV-A59 (11). While cleavage of the MHV S protein generally correlates strongly with cell-cell fusion (7), virus-cell fusion appears not to be affected by the prevention of S protein cleavage, indicating that these fusion events have different requirements (11).The amino-terminal S...

mentioning

confidence: 95%

Murine Coronavirus with an Extended Host Range Uses Heparan Sulfate as an Entry Receptor

Lintelo

et al. 2005

125

169

“…Of these GAGs, HS has been identified as an attachment factor for a number of viruses and, unlike other GAGs, is abundantly expressed on most cell types (28). We first evaluated whether RVFV ns infection could be inhibited by inclusion of soluble heparin, a GAG analogue of HS, as a competitor in the inoculum (23). As a control virus, we used a nonspreading vesicular stomatitis virus (here referred to as VSV ns ), a VSV-⌬G/GFP recombinant virus pseudotyped with its authentic fusion glycoprotein G (5).…”

mentioning

confidence: 99%

Heparan Sulfate Facilitates Rift Valley Fever Virus Entry into the Cell

Boer

Kortekaas

et al. 2012

b Rift Valley fever virus (RVFV), an emerging arthropod-borne pathogen, has a broad host and cell tropism. Here we report that the glycosaminoglycan heparan sulfate, abundantly present on the surface of most animal cells, is required for efficient entry of RVFV. Entry was significantly reduced by preincubating the virus inoculum with highly sulfated heparin, by enzymatic removal of heparan sulfate from cells and in cells genetically deficient in heparan sulfate synthesis.

“…Next, we analyzed the ability of the virions of FCoV strains UCD1, UCD, and 79-1146 (30), the last being a serotype II FCoV, to bind to heparin-agarose beads. Heparin, a product of mast cells, is commonly used as an analog of cellular heparan sulfate in receptor-ligand interaction assays (25). Similar quantities of the virions, as determined by quantitative TaqMan RT-PCR (19), were incubated for 1 h at 4°C with the heparinagarose beads in the presence or absence of heparin (500 ng/ml; added 1 h before addition of the beads).…”

mentioning

confidence: 99%

Cleavage of Group 1 Coronavirus Spike Proteins: How Furin Cleavage Is Traded Off against Heparan Sulfate Binding upon Cell Culture Adaptation

Haijema

Schellen

et al. 2008

103

107

A longstanding enigmatic feature of the group 1 coronaviruses is the uncleaved phenotype of their spike protein, an exceptional property among class I fusion proteins. Here, however, we show that some group 1 coronavirus spike proteins carry a furin enzyme recognition motif and can actually be cleaved, as demonstrated for a feline coronavirus. Interestingly, this feature can be lost during cell culture adaptation by a single mutation in the cleavage motif; this, however, preserves a heparan sulfate binding motif and renders infection by the virus heparan sulfate dependent. We identified a similar cell culture adaptation for the human coronavirus OC43.Enveloped viruses use different types of fusion proteins to realize the membrane fusion by which they initiate their infection. For coronaviruses, it is the spike (S) protein that is responsible for cell entry, and this S protein has been shown to belong to the class I fusion proteins (4). These proteins typically occur in virions as homotrimeric complexes primed for fusion through cleavage by furin-like enzymes. Membrane fusion by these activated proteins can then be triggered upon receptor binding (e.g., human immunodeficiency virus type 1) or by conditions such as low pH after endosomal uptake (e.g., influenza A virus) (for a recent review, see reference 50).One of the puzzling questions about coronavirus S proteinmediated membrane fusion regards the cleavage requirement of the S protein. Coronaviruses have been assigned to different groups based on antigenic and genetic criteria (41). Interestingly, while the group 1 coronaviruses carry uncleaved S proteins, the S proteins of almost all viruses from groups 2 and 3 are furin activated (10) by processing at a characteristic multibasic motif (often RRXRR) present in these proteins. The importance of cleavage for infectivity was underscored recently by the revelation that the two prominent group 2 viruses lacking such a furin recognition site, and hence carrying uncleaved spikes, appeared to depend on a different, new processing mechanism. Thus, the severe acute respiratory syndrome coronavirus (SARS-CoV) and the murine hepatitis virus strain 2 (MHV-2) were both shown to require proteolytic cleavage in their target cell, which is mediated by cathepsin enzymes (23,36,42). The cathepsin cleavage site of the SARS-CoV spike protein was mapped to the same region as that in which, in other viruses, the S protein is activated by furin (B. J. Bosch and P. J. M. Rottier, unpublished observations), hence similarly generating an amino-terminal, receptor binding domain (S1) and a membrane-anchored carboxy-terminal domain (S2) responsible for membrane fusion (for reviews, see references 3 and 9).When looking closer into the enigmatic lack of cleavage of the group 1 coronavirus spike proteins, we established that the infection of cells by two of those viruses, human coronavirus (HCoV) NL63 (23) and feline infectious peritonitis virus strain 79-1146 (our unpublished observations), is insensitive to cathepsin inhibitors. However, w...