title: Insertion of heme b into the structure of the Cys34-carbamidomethylated human lipocalin α(1)-microglobulin: formation of a [(heme)(2) (α(1)-Microglobulin)](3) complex.
abstract: α(1)-Microglobulin (α(1)m) is a 26 kDa plasma and tissue protein belonging to the lipocalin protein family. Previous investigations indicate that the protein interacts with heme and suggest that it has a function in heme metabolism. However, detailed characterizations of the α(1)m-heme interactions are lacking. Here, we report for the first time the preparation and analysis of a stable α(1)m-heme complex upon carbamidomethylation of the reactive Cys34 by using recombinantly expressed human α(1)m. Analytical size-exclusion chromatography coupled with a diode-array absorbance spectrophotometry demonstrates that at first an α(1)m-heme monomer is formed. Subsequently, a second heme triggers oligomerization that leads to trimerization. The resulting (α(1)m[heme](2))(3) complex was characterized by resonance Raman and EPR spectroscopy, which support the presence of two ferrihemes, thus indicating an unusual spin-state admixed ground state with S=(3)/(2), (5)/(2).
authors.affiliation: Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
authors.forename: Judith F
authors.initials: JF
authors.lastname: Siebel
authors.forename: Robyn L
authors.initials: RL
authors.lastname: Kosinsky
authors.forename: Bo
authors.initials: B
authors.lastname: Åkerström
authors.forename: Markus
authors.initials: M
authors.lastname: Knipp
mesh_terms: D000510:Alpha-Globulins / Q000737:chemistry* / Q000378:metabolism; D002850:Chromatography, Gel / Q000379:methods; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D054834:Lipocalins / Q000737:chemistry* / Q000378:metabolism; D017510:Protein Folding; D013053:Spectrophotometry
chemical_list: D000510:Alpha-Globulins; D054834:Lipocalins; C016001:alpha-1-microglobulin; D006418:Heme