Disease relevance of NSP2

• Human group C rotavirus NSP2 has two hydrophobic heptad repeat regions, a basic, RNA-binding domain and a basic, proline-rich region [1].
• NSP2 of the rotavirus group causing endemic infantile diarrhea (group A) was shown to self-assemble into large doughnut-shaped octamers with circumferential grooves and deep clefts containing nucleotide-binding histidine triad (HIT)-like motifs [2].
• The loss of NSP2 expression inhibited viroplasm formation, genome replication, virion assembly, and synthesis of the other viral proteins [3].
• NS2 shares these features with the nonstructural protein, NSP2, of rotavirus, which like BTV is a member of the family Reoviridae [4].
• Multimers of the bluetongue virus nonstructural protein, NS2, possess nucleotidyl phosphatase activity: similarities between NS2 and rotavirus NSP2 [4].

High impact information on NSP2

• Several RNA binding sites, resulting from the quaternary organization of NSP2 monomers, may be required for the helix destabilizing activity of NSP2 and its function during genome replication and packaging [5].
• Two rotavirus nonstructural proteins, NSP2 (with nucleoside triphosphatase, single-stranded RNA [ssRNA] binding and helix-destabilizing activities) and NSP5, are essential in these events [6].
• Consistent with the observation that both NSP5 and RNA share the same binding site on the NSP2 octamer, filter binding assays showed that NSP5 competes with ssRNA binding, indicating that one of the functions of NSP5 is to regulate NSP2-RNA interactions during genome replication [6].
• Hyperphosphorylation of the rotavirus NSP5 protein is independent of serine 67, [corrected] NSP2, or [corrected] the intrinsic insolubility of NSP5 is regulated by cellular phosphatases [7].
• Histidine Triad-like Motif of the Rotavirus NSP2 Octamer Mediates both RTPase and NTPase Activities [8].

Biological context of NSP2

• This possibility was addressed in this report by using two forms of NSP5-green fluorescent protein (GFP) chimeras wherein GFP is fused at either the N or the C terminus of NSP5 (GFP-NSP5 and NSP5-GFP) and evaluating their VLS-forming capability (by light and electron microscopy) and phosphorylation and multimerization potential independent of NSP2 [9].
• Our results indicate that the octamer is the fully functional form of NSP2 and the form required for productive virus replication [10].
• Sequence analysis has indicated that an A152V mutation in NSP2 is responsible for the ts phenotype of tsE [10].
• Recently, we have demonstrated direct interaction of NSP5 with NSP2, and as a consequence of that, up-regulation of NSP5 hyperphosphorylation [11].
• In addition, in transient transfection assays, NSP5 phosphorylation in vivo was enhanced by co-expression of NSP2 [12].

Anatomical context of NSP2

• The gene 8 product of SA11 rotavirus, NS35 (NSP2), is a nonspecific RNA-binding protein that accumulates in cytoplasmic inclusions (viroplasms) and is required for genome replication [13].
• Association of rotavirus viroplasms with microtubules through NSP2 and NSP5 [14].

Associations of NSP2 with chemical compounds

• NSP5 interacts with NSP2 and undergoes a complex posttranslational hyperphosphorylation, generating species with reduced polyacrylamide gel electrophoresis mobility [15].
• Earlier studies reported that NSP5 is not hyperphosphorylated without NSP2 coexpression or deleting the NSP5 N terminus and that serine 67 is essential for NSP5 hyperphosphorylation [7].
• However, exposure to Mg(2+) and the nonpermissive temperature caused disruption of the tsE octamers and yielded the formation of polydisperse NSP2 aggregates, events not observed with wt octamers [10].

Other interactions of NSP2

• Published data and the interaction demonstrated here suggest a possible role for NSP5 as an adapter between NSP2 and the replication complex VP2-VP1-VP3 in core assembly and RNA encapsidation, modulating the role of NSP2 as a molecular motor involved in the packaging of viral mRNA [16].
• Viral proteins involved in RNA replication include the RNA polymerase (VP1), the core scaffold protein (VP2) and the non-structural RNA-binding proteins (NSP2 and NSP5) [17].

Analytical, diagnostic and therapeutic context of NSP2

• Cryoelectron Microscopy Structures of Rotavirus NSP2-NSP5 and NSP2-RNA Complexes: Implications for Genome Replication [6].
• Analytical ultracentrifugation showed that tsE NSP2 formed octamers which, like those formed by wild-type (wt) NSP2, undergo conformational change into more compact structures upon binding of nucleotides [10].
• The interaction between NSP2 and a series of NSP5 mutants was investigated using two different assays, a yeast two-hybrid system and an in vivo binding/immunoprecipitation assay [18].

References