Nuclear receptor structure/function features

Peroxisome Proliferator-Activated Receptors. Figure 1 Common structural and functional features of nuclear receptor transcription factors. Consistent with other members of the nuclear receptor superfamily, the PPARs have a modular domain structure consisting of domains A/B, C, D, and E. Each domain is associated with specific functions. 

Although ecdysone is the only steroid hormone in Drosophila of which the function is known, the haemolymph of the fly contains many other ecdysteroids, the function of which remains to be clarified. The haemolymph also contains the sesquiterpenoid, juvenile hormone (JH). In many insects, JH r ulates ecdysone release. JH has structural features in common with the retinoids and may signal through a nuclear RXR receptor. 

The presence of a carboxyl terminal group is necessary for binding to CRABP and for retinoid activity [2]. However, comparison of other retinoid structural features shows a lack of correlation between retinoid potency and affinity for CRABP. Some potent retinoids do not bind to CRABP but do bind to nuclear retinoid receptors such as the RARs [146-149]. One such retinoid has been reported to be equally or more potent than RA but has lower affinity for RARs than RA [149]. It has been suggested that the reason for this apparent anomaly may be that the potency of RA is reduced because of its ability to bind to endogenous CRABP. It appears, therefore, that one of the functions of CRABP may be to regulate the amount of intracellular-active RA and thus control quantitatively the intensity of biological effects [149]. ... 

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