Mutants created by site-directed mutagenesis were used to elucidate the function of amino acids involved in ligand binding to ecdysteroid receptor (EcR) and heterodimer formation with ultraspiracle (USP). The results demonstrate the importance of the C-terminal part of the D-domain and helix 12 of EcR for hormone binding. Some amino acids are involved either in ligand binding to EcR (E476, M504, D572, I617, N626) or ligand-dependent heterodimerization as determined by gel mobility shift assays (A612, L615, T619), while others are involved in both functions (K497, E648). Some amino acids are suboptimal for ligand binding (L615, T619), but mediate ligand-dependent dimerization. We conclude that the enhanced regulatory potential by ligand-dependent modulation of dimerization in the wild type is achieved at the expense of optimal ligand binding. Mutation of amino acids (K497, E648) involved in the salt bridge between helix 4 and 12 impair ligand binding to EcR more severely than hormone binding to the heterodimer, indicating that to some extent heterodimerization compensates for the deleterious effect of certain mutations. Different effects of the same point mutations on ligand binding to EcR and EcR/USP (R511, A612, L615, I617, T619, N626) indicate that the ligand-binding pocket is modified by heterodimerization.

α-Antitrypsin deficiency (AATD) is a genetically determined disorder that is associated with different clinical manifestations. We aimed to assess the prevalence of diagnosed AATD and its comorbidities using a large healthcare database.In this retrospective longitudinal observational study, we analysed data from 4 million insurants. Using International Classification of Diseases revision 10 (ICD-10) codes, we assessed the prevalence, comorbidities and healthcare utilisation of AATD patients (E88.0 repeatedly coded) relative to non-AATD patients with chronic obstructive pulmonary disease (COPD), emphysema or asthma.In our study population, we identified 673 AATD patients (590 aged ≥30 years), corresponding to a prevalence of 23.73 per 100 000 in all age groups and 29.36 per 100 000 in those ≥30 years. Based on the number of AATD cases detected in the sample size (673 out of 2 836 585), we extrapolated that there were 19 162 AATD cases in Germany during the years studied. AATD patients had a higher prevalence of arterial hypertension, chronic kidney disease and diabetes relative to non-AATD asthma or emphysema patients. When compared to non-AATD COPD patients, AATD patients had significantly more consultations and more frequent and longer hospitalisations.Our data strengthen the assumption that AATD is associated with a variety of other diseases. Healthcare utilisation appears to be higher among AATD patients as compared to patients with non-AATD-related obstructive lung diseases.

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The insect ecdysteroid receptor consists of a heterodimer between EcR and the RXR-orthologue, USP. We addressed the question of whether this heterodimer, like all other RXR heterodimers, may be formed in the absence of ligand and whether ligand promotes dimerization. We found that C-terminal protein fragments that comprised the ligand binding, but not the DNA binding domain of EcR and USP and which were equipped with the activation or DNA binding region of GAL4, respectively, exhibit a weak ability to interact spontaneously with each other. Moreover, the heterodimer formation is greatly enhanced upon administration of active ecdysteroids in a dose-dependent manner. This was shown in vivo by a yeast two-hybrid system and in vitro by a modified electromobility shift assay. Furthermore, the EcR fragment expressed in yeast was functional and bound radioactively labelled ecdysteroid specifically. Ligand binding was greatly enhanced by the presence of a USP ligand binding domain. Therefore, ecdysteroids are capable of inducing heterodimer formation between EcR and USP, even when the binding of these receptor proteins to cognate DNA response elements does not occur. This capability may be a regulated aspect of ecdysteroid action during insect development.Keywords: Drosophila melanogaster; yeast; two-hybrid; ecdysone receptor; dimerization; ultraspiracle.Ecdysteroids are widespread steroid hormones found in invertebrates [1] and plants [2,3] that regulate a variety of developmental, physiological, and reproductive processes [1,3]. Among insects, these hormones regulate the expression of genes through a highly orchestrated and coordinated transcriptional network [4][5][6]. The widespread and diverse effects of ecdysteroids on transcriptional regulation have served as a powerful model for investigating the diverse mechanisms by which steroid hormones, acting via nuclear receptors, exert their effects on a variety of life processes [4,7].The ecdysone receptor (EcR) [8], responsible for mediating these responses, occupies a special position among nuclear hormone receptors because it shows a unique combination of characteristics [9]. Unlike the vertebrate steroid receptors [10][11][12], EcR heterodimerizes with the insect RXR orthologue, ultraspiracle (USP) [13][14][15]. Nevertheless, while other nuclear receptors that dimerize with RXR normally are bound to DNA response elements already in their nonliganded state [11,16], this apparently is not true for the EcR/USP heterodimer (see however, [17]). Immunostaining has shown that the polytene chromosomes of a Chironomid or Sciarid are devoid of EcR/USP signals when prepared from developmental stages associated with low ecdysteroid titers [18,19]. A short in vitro incubation of the tissues with 20-hydroxyecdysone, however, is followed by the appearance of immunostaining signals at known ecdysteroid-responsive gene loci [18,19]. The affinity of EcR/USP dimers for ecdysone response elements (EcREs) clearly increases in the presence of the ecdysteroid muristerone A as demonstrated...

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