Characterization of Human Thioredoxin-like 2

Abstract

We describe here the cloning and characterization of a novel member of the thioredoxin family, thioredoxinlike protein 2 (Txl-2). The Txl-2 open reading frame codes for a protein of 330 amino acids consisting of two distinct domains: an N-terminal domain typical of thioredoxins and a C-terminal domain belonging to the nucleoside-diphosphate kinase family, separated by a small interface domain. The Txl-2 gene spans ϳ28 kb, is organized into 11 exons, and maps at locus 3q22.3-q23. A splicing variant lacking exon 5 (⌬5Txl-2) has also been isolated. By quantitative real time PCR we demonstrate that Txl-2 mRNA is ubiquitously expressed, with testis and lung having the highest levels of expression. Unexpectedly, light and electron microscopy analyses show that the protein is associated with microtubular structures such as lung airway epithelium cilia and the manchette and axoneme of spermatids. Using in vitro translated proteins, we demonstrate that full-length Txl-2 weakly associates with microtubules. In contrast, ⌬5Txl-2 specifically binds with very high affinity brain microtubule preparations containing microtubule-binding proteins. Importantly, ⌬5Txl-2 also binds to pure microtubules, proving that it possesses intrinsic microtubule binding capability. Taken together, ⌬5Txl-2 is the first thioredoxin reported to bind microtubules and might therefore be a novel regulator of microtubule physiology.

Spermatocyte/Spermatid-specific Thioredoxin-3, a Novel Golgi Apparatus-associated Thioredoxin, Is a Specific Marker of Aberrant Spermatogenesis

“…However, a positive control overexpressing human TRX-1 resulted in a 2-fold increase in enzymatic activity. The lack of activity of recombinant SPTRX-3 parallels that of SPTRX-2 and TXL-2 (9,20), two other proteins located in spermatozoa, which suggests that other testis-specific factors might be required in the assay mix.…”

“…Eukaryotic organisms have two ubiquitously expressed thioredoxin systems, one in cytoplasm composed of the Trx-1 and TrxR-1, and the other in mitochondria formed by Trx-2 and TrxR-2 (3). Furthermore, a large number of different thioredoxins with novel properties, such as organelle-specific localization in endoplasmic reticulum (6,7), tissue-specific distribution (8), and microtubule-binding properties (9), have recently been reported in mammals. This complexity is paralleled by the increasing number of splicing variants of both thioredoxin reductase genes.…”

The Nucleoside Diphosphate Kinase D (NM23-H4) Binds the Inner Mitochondrial Membrane with High Affinity to Cardiolipin and Couples Nucleotide Transfer with Respiration

“…Associated in networks with other nucleotide-metabolizing enzymes such as adenylate kinases, creatine kinases, and glycolytic enzymes, NDPKs participate in high energy phosphoryl transfer and signal communication in the cell (2). Up to now nine genes encoding NDPK or NDPK-like proteins have been identified (3,4), but little is known about their respective role within the cell. The most studied, NDPK-A and -B, encoded by NME1 and NME2 genes, respectively, play a key role in tumor progression and metastasis dissemination (5,6).…”

A common variant in combination with a nonsense mutation in a member of the thioredoxin family causes primary ciliary dyskinesia

“…In humans, this protein family comprises at least nine members that can be divided into two sets according to their sequence: while group I is composed of proteins that share high homology with each other and have the classic enzymatic activity of an NDK (i.e., NME1 to NME4), members of group II (i.e., NME5 to NME7, TXNDC3, and TXNDC6) are less conserved, and enzymatic activity has been demonstrated only for NME6. Of particular interest, members of group II share high homology with the NDK domains of the sea urchin IC1 chain, and, except for NME6, they are mainly expressed in testis (31,32). Within the NDK family, TXNDC3 and TXNDC6 are the only two proteins containing an NDK domain and a thioredoxin domain.…”