Anomeric specificity and protein-substrate interactions support the 3D model for the hemagglutinin-neuraminidase from Sendai virus

The 3D structure of paramyxovirus hemagglutinin-neuraminidase has not yet b een resolved; however, a theoretical model has been built by using influenz a virus and bacterial neuraminidases as template [V. C. Epa (1997) Proteins Struct. Funct. Gen. 29, 264-281]. Two common features of the catalytic mec hanism of the neuraminidases of known 3D structure are the anomeric specifi city and the involvement of a tyrosine residue in the stabilization of the transition state. These key features have been investigated on the water-so luble ectodomain of the hemagglutinin-neuraminidase from Sendai virus (cHN) . The anomeric specificity of the hydrolysis of the substrate by cHN has be en investigated by MMR spectroscopy. The immediate product of the reaction was the alpha-anomer, meaning that cHN belongs between glycohydrolases reta ining anomeric configuration like influenza virus neuraminidase. Measuremen ts of the UV difference spectrum upon binding of the substrate analogue 2,3 -dehydro 2-deossi N-acetyl neuraminic acid indicate the ionization of a tyr osine residue and decreased polarity in the environment of a tryptophan res idue. Functional significance of the spectral data was derived from the kno wn structure of influenza neuraminidase, where a tyrosinate ion is involved in the stabilization of the transition-state carbonium ion, and a tryptoph an residue is involved in the binding of the acetyl moiety of the substrate . The data give experimental support to the 3D model of paramyxovirus neura minidase. (C) 1999 Academic Press.