title: Red blood with blue-blood ancestry: intriguing structure of a snail hemoglobin.
abstract: The phylogenetic enigma of snail hemoglobin, its isolated occurrence in a single gastropod family, the Planorbidae, and the lack of sequence data, stimulated the present study. We present here the complete cDNA and predicted amino acid sequence of two hemoglobin polypeptides from the planorbid Biomphalaria glabrata (intermediate host snail for the human parasite Schistosoma mansoni). Both isoforms contain 13 different, cysteine-free globin domains, plus a small N-terminal nonglobin "plug" domain with three cysteines for subunit dimerization (total M(r) approximately 238 kDa). We also identified the native hemoglobin molecule and present here a preliminary 3D reconstruction from electron microscopical images (3 nm resolution); it suggests a 3 x 2-mer quaternary structure (M(r) approximately 1.43 MDa). Moreover, we identified a previously undescribed rosette-like hemolymph protein that has been mistaken for hemoglobin. We also detected expression of an incomplete hemocyanin as trace component. The combined data show that B. glabrata hemoglobin evolved from pulmonate myoglobin, possibly to replace a less-efficient hemocyanin, and reveals a surprisingly simple evolutionary mechanism to create a high molecular mass respiratory protein from 78 similar globin domains.
authors.affiliation: Institute of Zoology, Johannes Gutenberg University, D-55099 Mainz, Germany. lieb@uni-mainz.de
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lieb
authors.forename: Konstantina
authors.initials: K
authors.lastname: Dimitrova
authors.forename: Hio-Sun
authors.initials: HS
authors.lastname: Kang
authors.forename: Sabrina
authors.initials: S
authors.lastname: Braun
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gebauer
authors.forename: Andreas
authors.initials: A
authors.lastname: Martin
authors.forename: Ben
authors.initials: B
authors.lastname: Hanelt
authors.forename: Steven A
authors.initials: SA
authors.lastname: Saenz
authors.forename: Coen M
authors.initials: CM
authors.lastname: Adema
authors.forename: Jürgen
authors.initials: J
authors.lastname: Markl
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001700:Biomphalaria; D019143:Evolution, Molecular; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics; D006458:Hemolymph / Q000737:chemistry; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008969:Molecular Sequence Data; D010802:Phylogeny; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D006454:Hemoglobins; D020033:Protein Isoforms