Synthetic peptides in the study of the interaction of rabies virus and the acetylcholine receptor

Abstract

The neurotropism of some viruses may be explained in part by the attachment of these viruses to host cell receptors that are present on or even largely restricted to neurons. Rabies virus is an RNA virus that, after a period of replication in muscle, gains access to the central nervous system, where it selectively infects certain neuronal populations. The nicotinic acetylcholine receptor occurs in high density at the neuromuscular junction and is present in the central nervous system. Although several different cell surface constituents may act as attachment determinants for rabies, direct binding of radioactively labeled virus to affinity-purified acetylcholine receptor has been demonstrated. Binding of virus to the receptor was saturable and inhibited by up to 50% by alpha-bungarotoxin, a snake venom neurotoxin that binds at or near the acetylcholine binding site on the receptor. The molecular basis for the virus-receptor interaction may lie in an amino acid sequence similarity between the snake venom neurotoxins and a segment of the rabies virus glycoprotein. Two peptides (10 and 13 residues) of the rabies virus glycoprotein and homologous bungarotoxin peptides were synthesized and tested for ability to compete with labeled alpha-bungarotoxin for binding to the acetylcholine receptor. The peptides were found to compete with toxin binding with affinities comparable to those of the cholinergic ligands d-tubocurarine and nicotine. These findings indicate that a segment of the rabies virus glycoprotein interacts with the acetylcholine receptor at or near the acetylcholine binding site of the receptor. The similarity between the virus glycoprotein and the neurotoxin was further evidenced by the cross reaction of antibody raised against the virus 10-mer with the bungarotoxin 10-mer. Binding of rabies virus to the acetylcholine receptor or to other neuronal bungarotoxin-binding proteins may be related to the neurotropism of this virus. In addition, knowledge of both the region of the virus involved in binding and the binding domain on the receptor may be helpful in developing new strategies for treatment, especially for viruses that infect the central nervous system or evade the immune response through genetic drift. These strategies include development of antiviral agents that cross the blood-brain barrier and inhibit viral binding and the utilization as immunogens the regions of viruses, such as their binding domains, that are highly conserved among different strains.