Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 285, Issue 12, Pages 8855-8868Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M109.097063
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Funding
- National Institutes of Health, NIAID [R01 AI21389]
- National Institutes of Health [R01 GM62999, R01 GM081749]
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The rubella virus (RUBV) nonstructural (NS) protease domain, a Ca2+- and Zn2+-binding papain-like cysteine protease domain within the nonstructural replicase polyprotein precursor, is responsible for the self-cleavage of the precursor into two mature products, P150 and P90, that compose the replication complex that mediates viral RNA replication; the NS protease resides at the C terminus of P150. Here we report the Ca2+-dependent, stoichiometric association of calmodulin (CaM) with the RUBV NS protease. Co-immunoprecipitation and pull-down assays coupled with site-directed mutagenesis demonstrated that both the P150 protein and a 110-residue minidomain within NS protease interacted directly with Ca2+/CaM. The specific interaction was mapped to a putative CaM-binding domain. A 32-mer peptide (residues 1152-1183, denoted as RUBpep) containing the putative CaM-binding domain was used to investigate the association of RUBV NS protease with CaM or its N- and C-terminal subdomains. We found that RUBpep bound to Ca2+/CaM with a dissociation constant of 100-300 nM. The C-terminal subdomain of CaM preferentially bound to RUBpep with an affinity 12.5-fold stronger than the N-terminal subdomain. Fluorescence, circular dichroism and NMR spectroscopic studies revealed a wrapping around mode of interaction between RUBpep and Ca2+/CaM with substantially more helical structure in RUBpep and a global structural change in CaM upon complex formation. Using a site-directed mutagenesis approach, we further demonstrated that association of CaM with the CaM-binding domain in the RUBV NS protease was necessary for NS protease activity and infectivity.
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