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Journal of Virology, January 2006, p. 412-425, Vol. 80, No. 1
0022-538X/06/$08.00+0     doi:10.1128/JVI.80.1.412-425.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

N- and C-Terminal Cooperation in Rotavirus Enterotoxin: Novel Mechanism of Modulation of the Properties of a Multifunctional Protein by a Structurally and Functionally Overlapping Conformational Domain

Department of Microbiology and Cell Biology,¹ Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India²

Received 20 May 2005/ Accepted 4 October 2005

Rotavirus NSP4 is a multifunctional endoplasmic reticulum (ER)-resident nonstructural protein with the N terminus anchored in the ER and about 131 amino acids (aa) of the C-terminal tail (CT) oriented in the cytoplasm. Previous studies showed a peptide spanning aa 114 to 135 to induce diarrhea in newborn mouse pups with the 50% diarrheal dose approximately 100-fold higher than that for the full-length protein, suggesting a role for other regions in the protein in potentiating its diarrhea-inducing ability. In this report, employing a large number of methods and deletion and amino acid substitution mutants, we provide evidence for the cooperation between the extreme C terminus and a putative amphipathic -helix located between aa 73 and 85 (AAH_73-85) at the N terminus of N72, a mutant that lacked the N-terminal 72 aa of nonstructural protein 4 (NSP4) from Hg18 and SA11. Cooperation between the two termini appears to generate a unique conformational state, specifically recognized by thioflavin T, that promoted efficient multimerization of the oligomer into high-molecular-mass soluble complexes and dramatically enhanced resistance against trypsin digestion, enterotoxin activity of the diarrhea-inducing region (DIR), and double-layered particle-binding activity of the protein. Mutations in either the C terminus, AAH_73-85, or the DIR resulted in severely compromised biological functions, suggesting that the properties of NSP4 are subject to modulation by a single and/or overlapping highly sensitive conformational domain that appears to encompass the entire CT. Our results provide for the first time, in the absence of a three-dimensional structure, a unique conformation-dependent mechanism for understanding the NSP4-mediated pleiotropic properties including virus virulence and morphogenesis.

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