4573
To further identify the residues responsible for the activity , we isolated the mutant viruses that were not neutralized with the soluble form of MHV receptor proteins , since such mutants were expected to have mutations in amino acids responsible for receptor - binding activity .
 GENE: MHV receptor proteins
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
 GENE: MHV receptor proteins