Dynamics of MutS–Mismatched DNA Complexes Are Predictive of Their Repair Phenotypes

MutS recognizes base–base mismatches and base insertions/deletions (IDLs) in newly replicated DNA. Specific interactions between MutS and these errors trigger a cascade of protein–protein interactions that ultimately lead to their repair. The inability to explain why different DNA errors are repaired with widely varying efficiencies <i>in vivo</i> remains an outstanding example of our limited knowledge of this process. Here, we present single-molecule Förster resonance energy transfer measurements of the DNA bending dynamics induced by <i>Thermus aquaticus</i> MutS and the E41A mutant of MutS, which is known to have error specific deficiencies in signaling repair. We compared three DNA mismatches/IDLs (T-bulge, GT, and CC) with repair efficiencies ranging from high to low. We identify three dominant DNA bending states [slightly bent/unbent (<b>U</b>), intermediately bent (<b>I</b>), and significantly bent (<b>B</b>)] and find that the kinetics of interconverting among states varies widely for different complexes. The increased stability of MutS–mismatch/IDL complexes is associated with stabilization of <b>U</b> and lowering of the <b>B</b> to <b>U</b> transition barrier. Destabilization of <b>U</b> is always accompanied by a destabilization of <b>B</b>, supporting the suggestion that <b>B</b> is a “required” precursor to <b>U</b>. Comparison of MutS and MutS-E41A dynamics on GT and the T-bulge suggests that hydrogen bonding to MutS facilitates the changes in base–base hydrogen bonding that are required to achieve the <b>U</b> state, which has been implicated in repair signaling. Taken together with repair propensities, our data suggest that the bending kinetics of MutS–mismatched DNA complexes may control the entry into functional pathways for downstream signaling of repair

We FRET so You Don’t Have To: New Models of the Lipoprotein Lipase Dimer

Lipoprotein lipase (LPL) is a dimeric enzyme that is responsible for clearing triglyceride-rich lipoproteins from the blood. Although LPL plays a key role in cardiovascular health, an experimentally derived three-dimensional structure has not been determined. Such a structure would aid in understanding mutations in LPL that cause familial LPL deficiency in patients and help in the development of therapeutic strategies to target LPL. A major obstacle to structural studies of LPL is that LPL is an unstable protein that is difficult to produce in the quantities needed for nuclear magnetic resonance or crystallography. We present updated LPL structural models generated by combining disulfide mapping, computational modeling, and data derived from single-molecule Förster resonance energy transfer (smFRET). We pioneer the technique of smFRET for use with LPL by developing conditions for imaging active LPL and identifying positions in LPL for the attachment of fluorophores. Using this approach, we measure LPL–LPL intermolecular interactions to generate experimental constraints that inform new computational models of the LPL dimer structure. These models suggest that LPL may dimerize using an interface that is different from the dimerization interface suggested by crystal packing contacts seen in structures of pancreatic lipase

We FRET so You Don’t Have To: New Models of the Lipoprotein Lipase Dimer

Lipoprotein lipase (LPL) is a dimeric enzyme that is responsible for clearing triglyceride-rich lipoproteins from the blood. Although LPL plays a key role in cardiovascular health, an experimentally derived three-dimensional structure has not been determined. Such a structure would aid in understanding mutations in LPL that cause familial LPL deficiency in patients and help in the development of therapeutic strategies to target LPL. A major obstacle to structural studies of LPL is that LPL is an unstable protein that is difficult to produce in the quantities needed for nuclear magnetic resonance or crystallography. We present updated LPL structural models generated by combining disulfide mapping, computational modeling, and data derived from single-molecule Förster resonance energy transfer (smFRET). We pioneer the technique of smFRET for use with LPL by developing conditions for imaging active LPL and identifying positions in LPL for the attachment of fluorophores. Using this approach, we measure LPL–LPL intermolecular interactions to generate experimental constraints that inform new computational models of the LPL dimer structure. These models suggest that LPL may dimerize using an interface that is different from the dimerization interface suggested by crystal packing contacts seen in structures of pancreatic lipase

We FRET so You Don’t Have To: New Models of the Lipoprotein Lipase Dimer

Lipoprotein lipase (LPL) is a dimeric enzyme that is responsible for clearing triglyceride-rich lipoproteins from the blood. Although LPL plays a key role in cardiovascular health, an experimentally derived three-dimensional structure has not been determined. Such a structure would aid in understanding mutations in LPL that cause familial LPL deficiency in patients and help in the development of therapeutic strategies to target LPL. A major obstacle to structural studies of LPL is that LPL is an unstable protein that is difficult to produce in the quantities needed for nuclear magnetic resonance or crystallography. We present updated LPL structural models generated by combining disulfide mapping, computational modeling, and data derived from single-molecule Förster resonance energy transfer (smFRET). We pioneer the technique of smFRET for use with LPL by developing conditions for imaging active LPL and identifying positions in LPL for the attachment of fluorophores. Using this approach, we measure LPL–LPL intermolecular interactions to generate experimental constraints that inform new computational models of the LPL dimer structure. These models suggest that LPL may dimerize using an interface that is different from the dimerization interface suggested by crystal packing contacts seen in structures of pancreatic lipase

We FRET so You Don’t Have To: New Models of the Lipoprotein Lipase Dimer

Lipoprotein lipase (LPL) is a dimeric enzyme that is responsible for clearing triglyceride-rich lipoproteins from the blood. Although LPL plays a key role in cardiovascular health, an experimentally derived three-dimensional structure has not been determined. Such a structure would aid in understanding mutations in LPL that cause familial LPL deficiency in patients and help in the development of therapeutic strategies to target LPL. A major obstacle to structural studies of LPL is that LPL is an unstable protein that is difficult to produce in the quantities needed for nuclear magnetic resonance or crystallography. We present updated LPL structural models generated by combining disulfide mapping, computational modeling, and data derived from single-molecule Förster resonance energy transfer (smFRET). We pioneer the technique of smFRET for use with LPL by developing conditions for imaging active LPL and identifying positions in LPL for the attachment of fluorophores. Using this approach, we measure LPL–LPL intermolecular interactions to generate experimental constraints that inform new computational models of the LPL dimer structure. These models suggest that LPL may dimerize using an interface that is different from the dimerization interface suggested by crystal packing contacts seen in structures of pancreatic lipase