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@ARTICLE{Graen:315907,
      author       = {Graen, Timo and Inhester, Ludger and Clemens, Maike and
                      Grubmüller, Helmut and Groenhof, Gerrit},
      title        = {{T}he {L}ow {B}arrier {H}ydrogen {B}ond in the
                      {P}hotoactive {Y}ellow {P}rotein: {A} {V}acuum {A}rtifact
                      {A}bsent in the {C}rystal and {S}olution},
      journal      = {Journal of the American Chemical Society},
      volume       = {138},
      number       = {51},
      issn         = {1520-5126},
      address      = {Washington, DC},
      publisher    = {American Chemical Society},
      reportid     = {PUBDB-2016-06146},
      pages        = {16620 - 16631},
      year         = {2016},
      note         = {© American Chemical Society},
      abstract     = {There has been considerable debate on the existence of a
                      low-barrier hydrogen bond (LBHB) in the photoactive yellow
                      protein (PYP). The debate was initially triggered by the
                      neutron diffraction study of Yamaguchi et al. ( Proc. Natl.
                      Acad. Sci., U. S. A., 2009, 106, 440−444) who suggested a
                      model in which a neutral Arg52 residue triggers the
                      formation of the LBHB in PYP. Here, we present an
                      alternative model that is consistent within the error
                      margins of the Yamaguchi structure factors. The model
                      explains an increased hydrogen bond length without nuclear
                      quantum effects and for a protonated Arg52. We tested both
                      models by calculations under crystal, solution, and vacuum
                      conditions. Contrary to the common assumption in the field,
                      we found that a single PYP in vacuum does not provide an
                      accurate description of the crystal conditions but instead
                      introduces strong artifacts, which favor a LBHB and a large
                      1H NMR chemical shift. Our model of the crystal environment
                      was found to stabilize the two Arg52 hydrogen bonds and
                      crystal water positions for the protonated Arg52 residue in
                      free MD simulations and predicted an Arg52 pKa upshift with
                      respect to PYP in solution. The crystal and solution
                      environments resulted in almost identical 1H chemical shifts
                      that agree with NMR solution data. We also calculated the
                      effect of the Arg52 protonation state on the LBHB in 3D
                      nuclear equilibrium density calculations. Only the charged
                      crystal structure in vacuum supports a LBHB if Arg52 is
                      neutral in PYP at the previously reported level of theory (
                      J. Am. Chem. Soc., 2014, 136, 3542−3552). We attribute the
                      anomalies in the interpretation of the neutron data to a
                      shift of the potential minimum, which does not involve
                      nuclear quantum effects and is transferable beyond the
                      Yamaguchi structure.},
      cin          = {FS-CFEL-3},
      ddc          = {540},
      cid          = {I:(DE-H253)FS-CFEL-3-20120731},
      pnm          = {6211 - Extreme States of Matter: From Cold Ions to Hot
                      Plasmas (POF3-621)},
      pid          = {G:(DE-HGF)POF3-6211},
      experiment   = {EXP:(DE-MLZ)NOSPEC-20140101},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000391081800014},
      pubmed       = {pmid:27966904},
      doi          = {10.1021/jacs.6b05609},
      url          = {https://bib-pubdb1.desy.de/record/315907},
}