Frequency of D222G and Q223R Hemagglutinin Mutants of Pandemic (H1N1) 2009 Influenza Virus in Japan between 2009 and 2010

BACKGROUND: In April 2009, a novel swine-derived influenza A virus (H1N1pdm) emerged and rapidly spread around the world, including Japan. It has been suggested that the virus can bind to both 2,3- and 2,6-linked sialic acid receptors in infected mammals, in contrast to contemporary seasonal H1N1 viruses, which have a predilection for 2,6-linked sialic acid. METHODS/RESULTS: To elucidate the existence and transmissibility of α2,3 sialic acid-specific viruses in H1N1pdm, amino acid substitutions within viral hemagglutinin molecules were investigated, especially D187E, D222G, and Q223R, which are related to a shift from human to avian receptor specificity. Samples from individuals infected during the first and second waves of the outbreak in Japan were examined using a high-throughput sequencing approach. In May 2009, three specimens from mild cases showed D222G and/or Q223R substitutions in a minor subpopulation of viruses infecting these individuals. However, the substitutions almost disappeared in the samples from five mild cases in December 2010. The D187E substitution was not widespread in specimens, even in May 2009. CONCLUSIONS: These results suggest that α2,3 sialic acid-specific viruses, including G222 and R223, existed in humans as a minor population in the early phase of the pandemic, and that D222 and Q223 became more dominant through human-to-human transmission during the first and second waves of the epidemic. These results are consistent with the low substitution rates identified in seasonal H1N1 viruses in 2008

Molecular dynamics simulation of energy migration between tryptophan residues in apoflavodoxin

Molecular dynamics (MD) simulations over a 30 ns trajectory have been carried out on apoflavodoxin from Azotobacter vinelandii to compare with the published, experimental time-resolved fluorescence anisotropy results of F¨orster Resonance Energy Transfer (FRET) between the three tryptophan residues. MD analysis of atomic coordinates yielding both the time course of geometric parameters and the time-correlated second-order Legendre polynomial functions reflects immobilization of tryptophans in the protein matrix. However, one tryptophan residue (Trp167) undergoes flip-flop motion on the nanosecond timescale. The simulated time-resolved fluorescence anisotropy of tryptophan residues in apoflavodoxin implying a model of two unidirectional FRET pathways is in very good agreement with the experimental time-resolved fluorescence anisotropy, although the less efficient FRET pathway cannot be resolved and is hidden in the contribution of a slow protein motion

Molecular dynamics simulation of energy migration between tryptophan residues in apoflavodoxin

Molecular dynamics (MD) simulations over a 30 ns trajectory have been carried out on apoflavodoxin from Azotobacter vinelandii to compare with the published, experimental time-resolved fluorescence anisotropy results of F¨orster Resonance Energy Transfer (FRET) between the three tryptophan residues. MD analysis of atomic coordinates yielding both the time course of geometric parameters and the time-correlated second-order Legendre polynomial functions reflects immobilization of tryptophans in the protein matrix. However, one tryptophan residue (Trp167) undergoes flip-flop motion on the nanosecond timescale. The simulated time-resolved fluorescence anisotropy of tryptophan residues in apoflavodoxin implying a model of two unidirectional FRET pathways is in very good agreement with the experimental time-resolved fluorescence anisotropy, although the less efficient FRET pathway cannot be resolved and is hidden in the contribution of a slow protein motion

Proteins in Action: Femtosecond to Millisecond Structural Dynamics of a Photoactive Flavoprotein

[Image: see text] Living systems are fundamentally dependent on the ability of proteins to respond to external stimuli. The mechanism, the underlying structural dynamics, and the time scales for regulation of this response are central questions in biochemistry. Here we probe the structural dynamics of the BLUF domain found in several photoactive flavoproteins, which is responsible for light activated functions as diverse as phototaxis and gene regulation. Measurements have been made over 10 decades of time (from 100 fs to 1 ms) using transient vibrational spectroscopy. Chromophore (flavin ring) localized dynamics occur on the pico- to nanosecond time scale, while subsequent protein structural reorganization is observed over microseconds. Multiple time scales are observed for the dynamics associated with different vibrations of the protein, suggesting an underlying hierarchical relaxation pathway. Structural evolution in residues directly H-bonded to the chromophore takes place more slowly than changes in more remote residues. However, a point mutation which suppresses biological function is shown to ‘short circuit’ this structural relaxation pathway, suppressing the changes which occur further away from the chromophore while accelerating dynamics close to it