title: Quantitative comparison of human parainfluenza virus hemagglutinin-neuraminidase receptor binding and receptor cleavage.
abstract: The human parainfluenza virus (hPIV) hemagglutinin-neuraminidase (HN) protein binds (H) oligosaccharide receptors that contain N-acetylneuraminic acid (Neu5Ac) and cleaves (N) Neu5Ac from these oligosaccharides. In order to determine if one of HN's two functions is predominant, we measured the affinity of H for its ligands by a solid-phase binding assay with two glycoprotein substrates and by surface plasmon resonance with three monovalent glycans. We compared the dissociation constant (Kd) values from these experiments with previously determined Michaelis-Menten constants (Kms) for the enzyme activity. We found that glycoprotein substrates and monovalent glycans containing Neu5Acα2-3Galβ1-4GlcNAc bind HN with Kd values in the 10 to 100 μM range. Km values for HN were previously determined to be on the order of 1 mM (M. M. Tappert, D. F. Smith, and G. M. Air, J. Virol. 85:12146-12159, 2011). A Km value greater than the Kd value indicates that cleavage occurs faster than the dissociation of binding and will dominate under N-permissive conditions. We propose, therefore, that HN is a neuraminidase that can hold its substrate long enough to act as a binding protein. The N activity can therefore regulate binding by reducing virus-receptor interactions when the concentration of receptor is high.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
authors.forename: Mary M
authors.initials: MM
authors.lastname: Tappert
authors.forename: J Zachary
authors.initials: JZ
authors.lastname: Porterfield
authors.forename: Padmaja
authors.initials: P
authors.lastname: Mehta-D'Souza
authors.forename: Shelly
authors.initials: S
authors.lastname: Gulati
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Air
mesh_terms: D015707:HN Protein / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D010222:Parainfluenza Virus 1, Human / Q000201:enzymology*; D011485:Protein Binding; D011991:Receptors, Virus / Q000378:metabolism*; D020349:Surface Plasmon Resonance
chemical_list: D015707:HN Protein; C039111:HN protein receptor; D011991:Receptors, Virus