title: Introduction of a covalent histidine-heme linkage in a hemoglobin: a promising tool for heme protein engineering.
abstract: The hemoglobins of the cyanobacteria Synechococcus and Synechocystis (GlbNs) are capable of spontaneous and irreversible attachment of the b heme to the protein matrix. The reaction, which saturates the heme 2-vinyl by addition of a histidine residue, is reproduced in vitro by preparing the recombinant apoprotein, adding ferric heme, and reducing the iron to the ferrous state. Spontaneous covalent attachment of the heme is potentially useful for protein engineering purposes. Thus, to explore whether the histidine-heme linkage can serve in such applications, we attempted to introduce it in a test protein. We selected as our target the heme domain of Chlamydomonas eugametos LI637 (CtrHb), a eukaryotic globin that exhibits less than 50% sequence identity with the cyanobacterial GlbNs. We chose two positions, 75 in the FG corner and 111 in the H helix, to situate a histidine near a vinyl group. We characterized the proteins with gel electrophoresis, absorbance spectroscopy, and NMR analysis. Both T111H and L75H CtrHbs reacted upon reduction of the ferric starting material containing cyanide as the distal ligand to the iron. With L75H CtrHb, nearly complete (>90%) crosslinking was observed to the 4-vinyl as expected from the X-ray structure of wild-type CtrHb. Reaction of T111H CtrHb also occurred at the 4-vinyl, in a 60% yield indicating a preference for the flipped heme orientation in the starting material. The work suggests that the His-heme modification will be applicable to the design of proteins with a non-dissociable heme group.
authors.affiliation: T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: Selena L
authors.initials: SL
authors.lastname: Rice
authors.affiliation: T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Preimesberger
authors.affiliation: T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Johnson
authors.affiliation: T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA. Electronic address: lecomte_jtj@jhu.edu.
authors.forename: Juliette T J
authors.initials: JTJ
authors.lastname: Lecomte
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002696:Chlamydomonas / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006418:Heme / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D015202:Protein Engineering; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011524:Protoporphyrins / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D046940:Synechococcus / Q000737:chemistry; D046939:Synechocystis / Q000737:chemistry; D054793:Truncated Hemoglobins / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D010940:Plant Proteins; D011524:Protoporphyrins; D011994:Recombinant Proteins; D054793:Truncated Hemoglobins; C448299:iron protoporphyrin IX; D006418:Heme; D006639:Histidine
keywords: 2/2 Hemoglobin; Heme post-translational modification; Paramagnetic NMR spectroscopy; Protein engineering; Truncated hemoglobin