Dioxygenation of human serum albumin having a prosthetic heme group in a tailor-made heme pocket.
Human serum albumin (HSA) is the most abundant plasma protein in our bloodstream and serves as a transporter for small hydrophobic molecules such as fatty acids, bilirubin, and steroids. Hemin dissociated from methemoglobin is also bound within a narrow D-shaped cavity in subdomain IB of HSA. In terms of the general hydrophobicity of the alpha-helical pocket, HSA potentially has features similar to the heme-binding site of myoglobin (Mb) or hemoglobin (Hb). However, the reduced ferrous HSA-heme complex is immediately oxidized by O2, because HSA lacks the proximal histidine that enables the heme group to bind O2. In this paper, we report the introduction of a proximal histidine into the subdomain IB of HSA by site-directed mutagenesis to construct a tailor-made heme pocket (I142H/Y161L), which allows a reversible O2 binding to the prosthetic heme group. Laser flash photolysis experiments revealed that this artificial hemoprotein appears to have two different geometries of the axial-imidazole coordination, and these two species (I and II) showed rather low O2 binding affinities (P1/2O2 = 18 and 134 Torr) relative to those of Mb and Hb.
Komatsu
Teruyuki
T
Advanced Research Institute for Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan.
Ohmichi
Naomi
N
Zunszain
Patricia A
PA
Curry
Stephen
S
Tsuchida
Eishun
E
D001665:Binding Sites; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet
D011994:Recombinant Proteins; D012709:Serum Albumin; D006418:Heme; D010100:Oxygen