title: Geometric constraints for porphyrin binding in helical protein binding sites.
abstract: Helical bundles which bind heme and porphyrin cofactors have been popular targets for cofactor-containing de novo protein design. By analyzing a highly nonredundant subset of the protein databank we have determined a rotamer distribution for helical histidines bound to heme cofactors. Analysis of the entire nonredundant database for helical sequence preferences near the ligand histidine demonstrated little preference for amino acid side chain identity, size, or charge. Analysis of the database subdivided by ligand histidine rotamer, however, reveals strong preferences in each case, and computational modeling illuminates the structural basis for some of these findings. The majority of the rotamer distribution matches that predicted by molecular simulation of a single porphyrin-bound histidine residue placed in the center of an all-alanine helix, and the deviations explain two prominent features of natural heme protein binding sites: heme distortion in the case of the cytochromes C in the m166 histidine rotamer, and a highly prevalent glycine residue in the t73 histidine rotamer. These preferences permit derivation of helical consensus sequence templates which predict optimal side chain-cofactor packing interactions for each rotamer. These findings thus promise to guide future design endeavors not only in the creation of higher affinity heme and porphyrin binding sites, but also in the direction of bound cofactor geometry.
authors.affiliation: Department of Physics, the City College of New York, New York, New York 10031, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Negron
authors.forename: Christian
authors.initials: C
authors.lastname: Fufezan
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Koder
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003198:Computer Simulation; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism; D030562:Databases, Protein; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D006420:Hemeproteins / Q000737:chemistry* / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D011166:Porphyrins / Q000737:chemistry / Q000378:metabolism; D011422:Propionates / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary
chemical_list: D003574:Cytochrome c Group; D006420:Hemeproteins; D008024:Ligands; D011166:Porphyrins; D011422:Propionates; D006418:Heme; D006639:Histidine