title: Rational design of a three-heptad coiled-coil protein and comparison by molecular dynamics simulation with the GCN4 coiled coil: presence of interior three-center hydrogen bonds.
abstract: alpha-Helical coiled coils have a 7-residue repeating pattern (abcdefg) where a and d are usually hydrophobic. We have designed a 2-stranded 44-residue coiled-coil protein (P44) consisting of 2 22-residue alpha-helices linked by 2 terminal disulfide groups to test whether the disulfide bridges could stabilize a 3-heptad coiled coil. P44 should be stabilized by intrahelical hydrogen bonds, interhelical disulfide and salt bridges, and interior hydrophobic interactions. A computer model of P44 was built and its stability was studied by molecular dynamics simulation with explicit water. This doubly crosslinked 3-heptad coiled coil did not unfold during a 300-ps simulation with explicit water. This doubly crosslinked 3-heptad coiled coil did not unfold during a 300-ps simulation. But reduced P44 with 4 thiol groups did unfold. For comparison, the 62-residue crystal structure of the 4-heptad coiled coil of transcription activator GCN4 did not unfold during a 300-ps simulation. Thus P44 may be a stable folded protein in aqueous solution. These simulations revealed the presence of 2 local hydrogen bond networks involving intra-helical 3-center hydrogen bonds in the hydrophobic interior of the coiled coils of GCN4 and P44. The NH hydrogen at d makes a 3-center hydrogen bond whose major component is to the i - 4 C = O oxygen at g and minor component is to the solvent-inaccessible i - 3 C = O oxygen at a. Likewise, the NH hydrogen at g makes a 3-center hydrogen bond with the i - 4 C = O oxygen at c and the buried i - 3 C = O oxygen at d.
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel HIll 27599.
authors.forename: J E
authors.initials: JE
authors.lastname: Rozzelle
authors.forename: A
authors.initials: A
authors.lastname: Tropsha
authors.forename: B W
authors.initials: BW
authors.lastname: Erickson
mesh_terms: D000595:Amino Acid Sequence; D003198:Computer Simulation; D003460:Crystallization; D004268:DNA-Binding Proteins; D004220:Disulfides / Q000737:chemistry; D015195:Drug Design; D005656:Fungal Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D017510:Protein Folding; D011494:Protein Kinases / Q000737:chemistry*; D017433:Protein Structure, Secondary; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000737:chemistry*
chemical_list: D004268:DNA-Binding Proteins; D004220:Disulfides; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D011494:Protein Kinases