Thermal stability of the hemagglutinin-neuraminidase from Sendai virus evidences two folding domains

The domain structure of hemagglutinin-neuraminidase from Sendai virus (cHN) was investigated by studying the thermal stability in the 20-100 degreesC range. Differential scanning calorimetry evidences two conformational trans itions. The first transition:ls apparently a reversible two-state process, with T-m 48.3 degreesC, and is shifted to 50.1 degreesC in the presence of the substrate analogue 2,3-dehydro-2-deoxy-N-acetyl neuraminic acid, meanin g that the substrate binding domain is involved in the transition. The seco nd transition, with apparent T-m 53.2 degreesC, is accompanied by irreversi ble loss of enzymatic activity of the protein, and the presence of the subs trate analogue does not affect the T-m The data indicate that cHN is compos ed of two independent folding domains, and that only one domain is involved in the binding of the substrate. Our results suggest that the paramyxoviru s neuraminidases have the folding properties of a two-domain protein. (C) 2 001 Federation of European Biochemical Societies. Published by Elsevier Sci ence B.V. All rights reserved.