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1.  Structural Basis for the Modulation of the Neuronal Voltage-Gated Sodium Channel NaV1.6 by Calmodulin 
Scientific Reports  2013;3:2435.
The neuronal-voltage gated sodium channel (VGSC), NaV1.6, plays an important role in propagating action potentials along myelinated axons. Calmodulin (CaM) is known to modulate the inactivation kinetics of NaV1.6 by interacting with its IQ motif. Here we report the crystal structure of apo-CaM:NaV1.6IQ motif, along with functional studies. The IQ motif of NaV1.6 adopts an α-helical conformation in its interaction with the C-lobe of CaM. CaM uses different residues to interact with NaV1.6IQ motif depending on the presence or absence of Ca2+. Three residues from NaV1.6, Arg1902, Tyr1904 and Arg1905 were identified as the key common interacting residues in both the presence and absence of Ca2+. Substitution of Arg1902 and Tyr1904 with alanine showed a reduced rate of NaV1.6 inactivation in electrophysiological experiments in vivo. Compared with other CaM:NaV complexes, our results reveal a different mode of interaction for CaM:NaV1.6 and provides structural insight into the isoform-specific modulation of VGSCs.
PMCID: PMC3743062  PMID: 23942337
2.  Structural Basis for the Interaction of Unstructured Neuron Specific Substrates Neuromodulin and Neurogranin with Calmodulin 
Scientific Reports  2013;3:1392.
Neuromodulin (Nm) and neurogranin (Ng) are neuron-specific substrates of protein kinase C (PKC). Their interactions with Calmodulin (CaM) are crucial for learning and memory formation in neurons. Here, we report the structure of IQ peptides (24aa) of Nm/Ng complexed with CaM and their functional studies with full-length proteins. Nm/Ng and their respective IQ peptides are intrinsically unstructured; however, upon binding with CaM, IQ motifs adopt a helical conformation. Ser41 (Ser36) of Nm (Ng) is located in a negatively charged pocket in the apo CaM and, when phosphorylated, it will repel Nm/Ng from CaM. These observations explain the mechanism by which PKC-induced Ser phosphorylation blocks the association of Nm/Ng with CaM and interrupts several learning- and memory-associated functions. Moreover, the present study identified Arg as a key CaM interacting residue from Nm/Ng. This residue is crucial for CaM-mediated function, as evidenced by the inability of the Ng mutant (Arg-to-Ala) to potentiate synaptic transmission in CA1 hippocampal neurons.
PMCID: PMC3589724  PMID: 23462742
3.  Structural basis for the methylation of A1408 in 16S rRNA by a panaminoglycoside resistance methyltransferase NpmA from a clinical isolate and analysis of the NpmA interactions with the 30S ribosomal subunit 
Nucleic Acids Research  2010;39(5):1903-1918.
NpmA, a methyltransferase that confers resistance to aminoglycosides was identified in an Escherichia coli clinical isolate. It belongs to the kanamycin–apramycin methyltransferase (Kam) family and specifically methylates the 16S rRNA at the N1 position of A1408. We determined the structures of apo-NpmA and its complexes with S-adenosylmethionine (AdoMet) and S-adenosylhomocysteine (AdoHcy) at 2.4, 2.7 and 1.68 Å, respectively. We generated a number of NpmA variants with alanine substitutions and studied their ability to bind the cofactor, to methylate A1408 in the 30S subunit, and to confer resistance to kanamycin in vivo. Residues D30, W107 and W197 were found to be essential. We have also analyzed the interactions between NpmA and the 30S subunit by footprinting experiments and computational docking. Helices 24, 42 and 44 were found to be the main NpmA-binding site. Both experimental and theoretical analyses suggest that NpmA flips out the target nucleotide A1408 to carry out the methylation. NpmA is plasmid-encoded and can be transferred between pathogenic bacteria; therefore it poses a threat to the successful use of aminoglycosides in clinical practice. The results presented here will assist in the development of specific NpmA inhibitors that could restore the potential of aminoglycoside antibiotics.
PMCID: PMC3061052  PMID: 21062819
4.  Dimerization of Hepatitis E Virus Capsid Protein E2s Domain Is Essential for Virus–Host Interaction 
PLoS Pathogens  2009;5(8):e1000537.
Hepatitis E virus (HEV), a non-enveloped, positive-stranded RNA virus, is transmitted in a faecal-oral manner, and causes acute liver diseases in humans. The HEV capsid is made up of capsomeres consisting of homodimers of a single structural capsid protein forming the virus shell. These dimers are believed to protrude from the viral surface and to interact with host cells to initiate infection. To date, no structural information is available for any of the HEV proteins. Here, we report for the first time the crystal structure of the HEV capsid protein domain E2s, a protruding domain, together with functional studies to illustrate that this domain forms a tight homodimer and that this dimerization is essential for HEV–host interactions. In addition, we also show that the neutralizing antibody recognition site of HEV is located on the E2s domain. Our study will aid in the development of vaccines and, subsequently, specific inhibitors for HEV.
Author Summary
Infectious viral hepatitis is a major disease in both developing and developed countries. Hepatitis E virus (HEV) is one of the major causes of severe inflammation of the liver, which is characterized by jaundice, fever, liver enlargement, and abdominal pain in humans and non-human primates. The hepatitis E virus capsid is made up of individual subunits consisting of homodimers of a single structural protein forming the virus shell. These dimers are believed to protrude from the viral surface and to interact with host cells to initiate infection. To date, no structural information is available for any of the HEV proteins. This article reports the crystal structure of the HEV capsid protein domain E2s (protruding domain), along with functional studies, which illustrate the tight homodimeric state of E2s and that dimerization is essential for both HEV–host interactions and disease progression. We also show that the neutralizing antibody recognition site of HEV is located on the E2s domain. The present findings will aid the development of vaccines and novel inhibitors for HEV.
PMCID: PMC2714988  PMID: 19662165
5.  Structure and Evolutionary Origin of Ca2+-Dependent Herring Type II Antifreeze Protein 
PLoS ONE  2007;2(6):e548.
In order to survive under extremely cold environments, many organisms produce antifreeze proteins (AFPs). AFPs inhibit the growth of ice crystals and protect organisms from freezing damage. Fish AFPs can be classified into five distinct types based on their structures. Here we report the structure of herring AFP (hAFP), a Ca2+-dependent fish type II AFP. It exhibits a fold similar to the C-type (Ca2+-dependent) lectins with unique ice-binding features. The 1.7 Å crystal structure of hAFP with bound Ca2+ and site-directed mutagenesis reveal an ice-binding site consisting of Thr96, Thr98 and Ca2+-coordinating residues Asp94 and Glu99, which initiate hAFP adsorption onto the [10-10] prism plane of the ice lattice. The hAFP-ice interaction is further strengthened by the bound Ca2+ through the coordination with a water molecule of the ice lattice. This Ca2+-coordinated ice-binding mechanism is distinct from previously proposed mechanisms for other AFPs. However, phylogenetic analysis suggests that all type II AFPs evolved from the common ancestor and developed different ice-binding modes. We clarify the evolutionary relationship of type II AFPs to sugar-binding lectins.
PMCID: PMC1891086  PMID: 17579720

Results 1-5 (5)