Attaches the virus to sialic acid-containing cell receptors and thereby initiating infection. Binding of HN protein to the receptor induces a conformational change that allows the F protein to trigger virion/cell membranes fusion. Neuraminidase activity ensures the efficient spread of the virus by dissociating the mature virions from the neuraminic acid containing glycoproteins. Hydrolysis of alpha-(2->3)-, alpha-(2->6)-, alpha-(2->8)- glycosidic linkages of terminal sialic acid residues in oligosaccharides, glycoproteins, glycolipids, colominic acid and synthetic substrates. Homotetramer; composed of disulfide-linked homodimers (Probable). Interacts with F protein trimer. Folded in the endoplasmic reticulum. N-glycosylated; glycans consist of a mixture of high mannose-type oligosaccharides and of complex-type oligosaccharides. Belongs to the paramyxoviruses hemagglutinin-neuraminidase family.