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Venoms from scorpions contain extremely rich bioactive peptides that often carry diverse functions and are presumably needed to achieve synergistic effects for rapidly immobilizing prey and defending themselves. BotLVP1 is a unique heterodimer protein recently found in the scorpion Buthus occitanus tunetanus venom that is structurally related to scorpion toxins affecting sodium channels (NaScTxs) but exhibits adipocyte lipolysis activity. We have isolated and identified two cDNA clones encoding subunits α and β of a BotLVP1-like peptide (named BmLVP1) from the Chinese scorpion Buthus martensii venom gland and determined the first complete gene structure of this subfamily. These results highlight a genetic link between these lipolysis activating peptides and NaScTxs. Comparison of cDNA and genomic sequences combined with protein structural and functional analysis provides evidence supporting the existence of RNA editing mechanism in scorpion venom glands, which could mediate functional switch of BmLVP1 gene, from adipocyte lipolysis to neurotoxicity, by altering the wrapper disulfide bridge (WDB) pattern of the peptides.

From hemocytes of the tunicate Halocynthia aurantium we purified a new antimicrobial peptide named halocidin. The native peptide had a mass of 3443 Da and comprised two different subunits containing 18 amino acid residues (WLNALLHHGLNCAKGVLA) and 15 residues (ALLHHGLNCAKGVLA), which were linked covalently by a single cystine disulfide bond. Two different monomers were separately synthesized and used to make three additional isoforms (15 residue homodimer, 18 residue homodimer, heterodimer). In antimicrobial assays performed with synthetic peptides of halocidin, it was confirmed that congeners of the 18 residue monomer were more active than those of the 15 residue monomer against methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa.

Class I aminoacyl-tRNA synthetases have been thought to be single polypeptide enzymes. However, the complete genome sequence of a hyper thermophile Aquifex aeolicus suggests that the gene for leucyl-tRNA synthetases (LeuRS) is probably split into two pieces (leuS and leuS′). In this research, each gene was separately cloned and overexpressed in Escherichia coli and the protein products were examined for LeuRS activity. Leucylation activity was detected only when both gene products coexisted. Gel filtration analysis showed that the active form of A. aeolicus LeuRS has a heterodimeric (α/β type) quaternary structure that is unique among class I aminoacyl-tRNA synthetases.

S100A4 (Mts1) is a Ca2+-binding protein of the S100 family. This protein plays an important role in promoting tumor metastasis. In order to identify S100A4 interacting proteins, we have applied the yeast two-hybrid system as an in vivo approach. By screening a mouse mammary adenocarcinoma library, we have demonstrated that S100A4 forms a heterocomplex with S100A1, another member of the S100 family. The non-covalent heterodimerization was confirmed by fluorescence spectroscopy and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Mutational analysis revealed that replacement of Cys76 and/or Cys81 of S100A4 by Ser abolishes the S100A4/S100A1 heterodimerization, but does not affect the S100A4 homodimerization in vivo.

Liver X receptor (LXR)/retinoid X receptor (RXR) heterodimers have been shown to perform critical functions in cholesterol and lipid metabolism. Here, we have conducted a comparative analysis of the contributions of LXR and RXR binding to steroid receptor coactivator-1 (SRC-1), which contains three copies of the NR box. We demonstrated that the coactivator-binding surface of LXR, but not that of RXR, is critically important for physical and functional interactions with SRC-1, thereby confirming that RXR functions as an allosteric activator of SRC-1–LXR interaction. Notably, we identified NR box-2 and -3 as the essential binding targets for the SRC-1-induced stimulation of LXR transactivity, and observed the competitive in vitro binding of NR box-2 and -3 to LXR.Structured summaryMINT-7986678, MINT-7986639, MINT-7986700, MINT-7986720, MINT-7986736, MINT-7986760, MINT-7986787: LXR (uniprotkb:Q13133) physically interacts (MI:0915) with SRC1 (uniprotkb:Q15788) and RXR (uniprotkb:P19793) by pull down (MI:0096)MINT-7986596, MINT-7986621: SRC1 (uniprotkb:Q15788) physically interacts (MI:0915) with LXR (uniprotkb:Q13133) by pull down (MI:0096)MINT-7986555, MINT-7986575: LXR (uniprotkb:Q13133) physically interacts (MI:0915) with SRC1 (uniprotkb:Q15788) by two hybrid (MI:0018)MINT-7986808, MINT-7986907, MINT-7986890: SRC1 (uniprotkb:Q15788) binds (MI:0407) to LXR (uniprotkb:Q13133) by pull down (MI:0096)MINT-7986822, MINT-7986848, MINT-7986865: SRC1 (uniprotkb:Q15788) binds (MI:0407) to RXR (uniprotkb:P19793) by pull down (MI:0096)

An αβ heterodimer of the F 1 -ATPase of Rhodospirillum rubrum was isolated by extraction of chromatophores with LiCl. Each αβ heterodimer contains one tightly bound ADP, which is released upon removal of medium Mg 2+ . The dimer can be reversibly dissociated by removal of Mg 2+ -ions. The αβ heterodimer restores both ATP-synthetic and hydrolytic activities to LiCl-treated chromatophores, saturation being achieved at approximately 2 mmol αβ · mol BChl −1 . The heterodimer itself hydrolyses Mg-ATP with an activity distinct from RF 1 , being unaffected by azide or sulphite ions. The V max and K m (ATP) for this Mg 2+ -dependent activity were 110 ± 10 nmol · min −1 mg protein −1 and 100 ± 30 μM, respectively. The K m did not differ significantly from that of RF 1 .

Curculin from Curculigo latifolia is a unique sweet protein that exhibits both sweet-tasting and taste-modifying activities. We isolated a gene that encodes a novel protein highly homologous to curculin. Using cDNAs of the previously known curculin (designated as curculin1) and the novel curculin isoform (curculin2), we produced a panel of homodimeric and heterodimeric recombinant curculins by Escherichia coli expression systems. It was revealed that sweet-tasting and taste-modifying activities were exhibited solely by the heterodimer of curculin1 and curculin2.

To understand signaling by the neuregulin (NRG) receptor ErbB3/HER3, it is important to know whether ErbB3 forms homodimers upon ligand binding. Previous biophysical studies suggest that the ErbB3 extracellular region remains monomeric when bound to NRG. We used a chimeric receptor approach to address this question in living cells, fusing the extracellular region of ErbB3 to the kinase-active intracellular domain of ErbB1. The ErbB3/ErbB1 chimera responded to NRG only if ErbB2 was co-expressed in the same cells, whereas an ErbB4/ErbB1 chimera responded without ErbB2. We, therefore, suggest that ErbB3 is an obligate heterodimerization partner because of its inability to homodimerize.

Retinoid X receptor alpha (RXRalpha) can reveal diverse functions through forming a heterodimer with peroxisome proliferator-activated receptor alpha (PPARalpha). However, the mechanism of regulation of the cellular RXRalpha level is unclear. Thus, quantitative change of RXRalpha was investigated in mouse liver. Nuclear RXRalpha level was constitutively lower in PPARalpha-null mice than in wild-type mice. The level was also increased by clofibrate treatment in wild-type mice without a concomitant increase of RXRalpha mRNA, but not in PPARalpha-null mice. Pulse chase experiments demonstrated that the presence of PPARalpha and its activation by ligands significantly affected the stability of nuclear RXRalpha. These findings suggest a novel regulatory mechanism of nuclear RXRalpha in vivo.

A hepatocyte growth factor (HGF) that stimulates DNA synthesis of adult rat hepatocytes in primary culture was purified as a homogeneous material from platelets of 1000 rats by a four-step procedure: stimulation of its release from platelets by thrombin, cation-exchanger fast protein liquid chromatography (FPLC) on a Mono S column, heparin-Sepharose CL-6B chromatography, and reverse-phase HPLC on a C4 column. The purified HGF stimulated DNA synthesis of adult rat hepatocytes in primary culture at 1 ng/ml and was maximally effective at 5 ng/ml, being about twice as potent as EGF at this concentration. HGF did not stimulate DNA synthesis of Swiss 3T3 cells. It was found to be a beat- and acid-labile protein that was inactivated by reduction with dithiothreitol. The purified HGF had a molecular mass of 82 kDa, as estimated by SDS-PAGE, and was found to be a heterodimer which dissociated into a large subunit of 69 kDa and a small one of 34 kDa by SDS-PAGE under reducing conditions. These biological and chemical properties showed that HGF was not identical with any known growth factors, including platelet-derived growth factor (PDGF).

The class IIIa adenylyl cyclase (AC) Rv1625c from Mycobacterium tuberculosis forms homodimers with two catalytic centres, whereas the Paramecium guanylyl and mammalian ACs operate as pseudoheterodimers with one catalytic centre. The functional and structural relationship of the catalytic domains of these related class III cyclases was investigated. Point mutations introduced into Rv1625c to engineer a forskolin-binding pocket created a single heterodimeric catalytic centre, yet did not result in forskolin activation. Chimerization of these Rv1625c point mutants with corresponding mammalian AC domains was impossible. However, it was successful using a complemental Paramecium guanylyl cyclase domain and resulted in an AC. The data signify a divergence of structural and functional evolution in class III Acs.

Chloroplast fructose 1,6-bisphosphatase (FBPase) is activated by reduction of a regulatory disulfide through thioredoxin f (Trx f). In the course of this reduction a transient mixed disulfide is formed linking covalently Trx f with FBPase, which possesses three Cys on a loop structure, two of them forming the redox-active disulfide bridge. The goal of this study was to identify the Cys involved in the transient mixed disulfide. To stabilize this reaction intermediate, mutant proteins with modified active sites were used. We identified Cys-155 of the FBPase as the one engaged in the formation of the mixed disulfide intermediate with Cys-46 of Trx f.

Both estrogen receptor alpha (ERalpha) and the recently identified ERbeta are nuclear receptors that are activated by estrogen. It was reported that ERalpha and ERbeta form heterodimers. Here, we show that they activate transcription independently rather than synergistically via estrogen response elements (ERE). To show the cross-talk between ERalpha and ERbeta, we utilized dominant negative mutants of ERs constructed by C-terminal truncation. Interestingly, ERalpha1-530 inhibited transactivation not only by ERalpha but also by ERbeta, whereas ERbeta1-481 inhibited transactivation by ERalpha as well as by ERbeta. The GST pull-down assay also demonstrated the cross-interaction of these mutants with wild-type ERalpha and ERbeta. Thus, we found dominant negative mutants that block both ERalpha and ERbeta signaling pathways.