Characterization of Sptrx, a Novel Member of the Thioredoxin Family Specifically Expressed in Human Spermatozoa

• Published in: The Journal of biological chemistry 2001-08, Vol.276 (34), p.31567-31574
• Main Authors: Miranda-Vizuete, A, Ljung, J, Damdimopoulos, A E, Gustafsson, J A, Oko, R, Pelto-Huikko, M, Spyrou, G
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Base Sequence; Chromosome Mapping; Chromosomes, Human, Pair 18; Cloning, Molecular; DNA, Complementary; Genome, Human; Humans; Immunohistochemistry; Male; Membrane Proteins; Molecular Sequence Data; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Sequence Homology, Amino Acid; Spermatozoa - metabolism; spermiogenesis; Sptrx gene; Thioredoxins - chemistry; Thioredoxins - genetics; Thioredoxins - metabolism
• ISSN: 0021-9258; 1083-351X; 1083-351X
• DOI: 10.1074/jbc.M101760200

Thioredoxins (Trx) are small ubiquitous proteins that participate in different cellular processes via redox-mediated reactions. We report here the identification and characterization of a novel member of the thioredoxin family in humans, named Sptrx ( s perm-s p ecific trx ), the first with a tissue-specific distribution, located exclusively in spermatozoa. Sptrx open reading frame encodes for a protein of 486 amino acids composed of two clear domains: an N-terminal domain consisting of 23 highly conserved repetitions of a 15-residue motif and a C-terminal domain typical of thioredoxins. Northern analysis and in situ hybridization shows that Sptrx mRNA is only expressed in human testis, specifically in round and elongating spermatids. Immunostaining of human testis sections identified Sptrx protein in spermatids, while immunofluorescence and immunogold electron microscopy analysis demonstrated Sptrx localization in the cytoplasmic droplet of ejaculated sperm. Sptrx appears to have a multimeric structure in native conditions and is able to reduce insulin disulfide bonds in the presence of NADPH and thioredoxin reductase. During mammalian spermiogenesis in testis seminiferous tubules and later maturation in epididymis, extensive reorganization of disulfide bonds is required to stabilize cytoskeletal sperm structures. However, the molecular mechanisms that control these processes are not known. The identification of Sptrx with an expression pattern restricted to the postmeiotic phase of spermatogenesis, when the sperm tail is organized, suggests that Sptrx might be an important factor in regulating critical steps of human spermiogenesis.