title: Human spermatid-specific thioredoxin-1 (Sptrx-1) is a two-domain protein with oxidizing activity.
abstract: Spermatid-specific thioredoxin-1 (Sptrx-1) is the first member of the thioredoxin family of proteins with a tissue-specific expression pattern, found exclusively in the tail of elongating spermatids and spermatozoa. We describe here further biochemical characterization of human Sptrx-1 protein structure and enzymatic activity. In gel filtration chromatography human Sptrx-1 eluates as a 400 kDa protein consistent with either an oligomeric form, not maintained by intermolecular disulfide bonding, and/or a highly asymmetrical structure. Analysis of circular dichroism spectra of fragments 1-360 and 361-469 and comparison to spectra of full-length Sptrx-1 supports a two-domain organization with a largely unstructured N-terminal domain and a folded thioredoxin-like C-terminal domain. Functionally, Sptrx-1 behaves as an oxidant in vitro when using selenite, but not oxidized glutathione, as electron acceptor. This oxidizing enzymatic activity suggests that Sptrx-1 might govern the stabilization (by disulfide cross-linking) of the different structures in the developing tail of spermatids and spermatozoa.
authors.affiliation: Center for Biotechnology, Department of Biosciences at NOVUM, Karolinska Institutet, S-14157 Huddinge, Sweden.
authors.forename: Alberto
authors.initials: A
authors.lastname: Jiménez
authors.forename: Catrine
authors.initials: C
authors.lastname: Johansson
authors.forename: Johanna
authors.initials: J
authors.lastname: Ljung
authors.forename: Johan
authors.initials: J
authors.lastname: Sagemark
authors.forename: Kurt D
authors.initials: KD
authors.lastname: Berndt
authors.forename: Bin
authors.initials: B
authors.lastname: Ren
authors.forename: Gudrun
authors.initials: G
authors.lastname: Tibbelin
authors.forename: Rudolf
authors.initials: R
authors.lastname: Ladenstein
authors.forename: Thomas
authors.initials: T
authors.lastname: Kieselbach
authors.forename: Arne
authors.initials: A
authors.lastname: Holmgren
authors.forename: Jan Ake
authors.initials: JA
authors.lastname: Gustafsson
authors.forename: Antonio
authors.initials: A
authors.lastname: Miranda-Vizuete
mesh_terms: D002850:Chromatography, Gel; D002942:Circular Dichroism; D003460:Crystallization; D018360:Crystallography, X-Ray; D006801:Humans; D008297:Male; D008565:Membrane Proteins; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013087:Spermatids / Q000737:chemistry*; D013879:Thioredoxins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; C434954:TXNDC2 protein, human; D013879:Thioredoxins