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Q/E mutant SA11 NSP4_CCDQ/E mutant SA11 NSP4_CCD
Structural highlights
Publication Abstract from PubMedRotavirus (RV) nonstructural protein NSP4 is a virulence factor that disrupts cellular Ca2+ homeostasis and plays multiple roles regulating RV replication and the pathophysiology of RV-induced diarrhea. Although its native oligomeric state is unclear, crystallographic studies of the coiled-coil domain (CCD) of NSP4 from two different strains suggest that it functions as a tetramer or a pentamer. While the CCD of simian SA11 NSP4 forms a tetramer that binds Ca2+ at its core, the CCD of a human strain ST3 forms a pentamer lacking the bound Ca2+ despite the residues (E120 and Q123) that coordinate Ca2+-binding being conserved. In these previous studies, while the tetramer crystallized at neutral pH, the pentamer crystallized at low pH suggesting that preference for a particular oligomeric state is pH-dependent and that pH could influence Ca2+-binding. Here, we sought to examine if the CCD of NSP4 from a single RV strain can exist in two oligomeric states regulated by Ca2+ or pH. Biochemical, biophysical and crystallographic studies show that while the CCD of SA11 NSP4 exhibits high affinity binding to Ca2+ at neutral pH and forms a tetramer, at low pH, it does not bind Ca2+ and forms a pentamer, and the transition from tetramer to pentamer is reversible with pH. Mutational analysis shows that Ca2+ binding is necessary for the tetramer formation as an E120A mutant forms a pentamer. We propose that the structural plasticity of NSP4 regulated by pH and Ca2+ may form a basis for its pleiotropic functions during RV replication. IMPORTANCE: The non-structural protein NSP4 of rotavirus is a multifunctional protein that plays an important role in virus replication, morphogenesis and pathogenesis. Previous crystallography studies of the coiled-coil domain (CCD) of NSP4 from two different rotavirus strains showed two distinct oligomeric states - a Ca2+-bound tetrameric state and a Ca2+-free pentameric state. Whether NSP4 CCD from the same strain can exist in different oligomeric states, and what factors might regulate its oligomeric preferences are not known. This study used a combination of biochemical, biophysical and crystallography techniques and found that the NSP4 CCD can undergo a reversible transition from a Ca2+-bound tetramer to a Ca2+-free pentamer in response to changes in pH. From these studies, we hypothesize that this remarkable structural adaptability of the CCD forms a basis for the pleiotropic functional properties of NSP4. Structural Plasticity of the Coiled-coil Domain of Rotavirus NSP4.,Sastri NP, Viskovska M, Hyser JM, Tanner MR, Horton LB, Sankaran B, Prasad BV, Estes MK J Virol. 2014 Sep 17. pii: JVI.02227-14. PMID:25231315[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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