Newcastle disease virus protein, molecular model. This is a hemagglutinin-neuromidase (HN) protein that enables the virus to bind to and infect host cells. The structure shown here consists of two neuraminidase (NA) domains (blue and orange) either side of an N-terminal stalk domain (light blue and pink). This stalk domain consists of four helices forming a tetrameric structure. The Newcastle disease virus (NDV) causes a viral infection in birds that can be fatal. This virus has been studied in cancer research.