title: Characterization of deltoid, a chimeric protein containing the oligomerization site of hepatitis delta antigen.
abstract: Both forms of the hepatitis delta antigen (HDAg) encoded by hepatitis delta virus are active only as oligomers. Previous studies showed that quadrin, a synthetic 50-residue peptide containing residues 12-60 from the N-terminus of HDAg, interferes with HDAg oligomerization, forms an alpha-helical coiled coil in solution, and forms a novel square octamer in the crystal consisting of four antiparallel coiled-coil dimers joined at the corners by hydrophobic binding of oligomerization sites located at each end of the dimers. We designed and synthesized deltoid (CH3CO-[Cys23]HDAg-(12-27)-seryl-tRNA synthetae-(59-65)-[Cys42]HDAg-(34-60)-Tyr-NH2), a chimeric protein that structurally resembles one end of the quadrin dimer and contains a single oligomerization site. The 51-residue chain of deltoid contains a seven-residue alpha-hairpin loop in place of the remainder of the quadrin dimer plus Cys12 and Cys31 for forming an intrachain disulfide bridge. Reduced, unbridged deltoid (Tm=61 degrees C, DeltaG(H2O)=-1.7 kcal mol(-1)) was less stable to denaturation by heat or guanidine HCl than oxidized, intrachain disulfide-bridged deltoid (Tm>80 degrees C, DeltaG(H2O)=-2.6 kcal mol(-1)). Each form is an alpha-helical dimer that reversibly dissociates into two monomers (Kd=80 microM).
authors.affiliation: Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. matthew_saderholm@berea.edu
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Saderholm
authors.forename: Stanley M
authors.initials: SM
authors.lastname: Lemon
authors.forename: Bruce W
authors.initials: BW
authors.lastname: Erickson
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D019281:Dimerization; D019791:Guanidine / Q000494:pharmacology; D006508:Hepatitis Antibodies / Q000276:immunology; D035923:Hepatitis delta Antigens / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013696:Temperature; D017186:Titrimetry
chemical_list: D006508:Hepatitis Antibodies; D035923:Hepatitis delta Antigens; D011993:Recombinant Fusion Proteins; D019791:Guanidine