Resilin is a member of a family of elastic proteins that includes elastin, as well as gluten, gliadin, abductin and spider silks. Resilin is found in specialized regions of the cuticle of most insects, providing low stiffness, high strain and efficient energy storage; it is best known for its roles in insect flight and the remarkable jumping ability of fleas and spittle bugs. Previously, the Drosophila melanogaster CG15920 gene was tentatively identified as one encoding a resilin-like protein (pro-resilin). Here we report the cloning and expression of the first exon of the Drosophila CG15920 gene as a soluble protein in Escherichia coli. We show that this recombinant protein can be cast into a rubber-like biomaterial by rapid photochemical crosslinking. This observation validates the role of the putative elastic repeat motif in resilin function. The resilience (recovery after deformation) of crosslinked recombinant resilin was found to exceed that of unfilled synthetic polybutadiene, a high resilience rubber. We believe that our work will greatly facilitate structural investigations into the functional properties of resilin and shed light on more general aspects of the structure of elastomeric proteins. In addition, the ability to rapidly cast samples of this biomaterial may enable its use in situ for both industrial and biomedical applications.

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Sulfonation catalyzed by sulfotransferase enzymes plays an important role in chemical defense mechanisms against various xenobiotics but also bioactivates carcinogens. A major human sulfotransferase, SULT1A1, metabolizes and/or bioactivates many endogenous compounds and is implicated in a range of cancers because of its ability to modify diverse promutagen and procarcinogen xenobiotics. The crystal structure of human SULT1A1 reported here is the first sulfotransferase structure complexed with a xenobiotic substrate. An unexpected finding is that the enzyme accommodates not one but two molecules of the xenobiotic model substrate p-nitrophenol in the active site. This result is supported by kinetic data for SULT1A1 that show substrate inhibition for this small xenobiotic. The extended active site of SULT1A1 is consistent with binding of diiodothyronine but cannot easily accommodate ␤-estradiol, although both are known substrates. This observation, together with evidence for a disorder-order transition in SULT1A1, suggests that the active site is flexible and can adapt its architecture to accept diverse hydrophobic substrates with varying sizes, shapes and flexibility. Thus the crystal structure of SULT1A1 provides the molecular basis for substrate inhibition and reveals the first clues as to how the enzyme sulfonates a wide variety of lipophilic compounds.Sulfonation is a widely distributed biological reaction catalyzed by members of the supergene family of enzymes called sulfotransferases (SULTs).1 SULTs utilize the sulfonate donor 3Ј-phosphoadenosine 5Ј-phosphosulfate (PAPS) to catalyze sulfonation, yielding PAP as the desulfonated product of the reaction. These enzymes modify the biological activities of a diverse range of compounds including neurotransmitters, hormones, and drugs. The reaction aids excretion of foreign chemicals but, in some cases, causes bioactivation of carcinogens and mutagens (1-3). SULTs are the focus of intense research in the fields of cancer, drug metabolism, and pharmacogenetics because genetic variation, particularly in isoenzyme SULT1A1, may predispose to lung cancers (4), protect against colorectal cancers (5), and affect the age of onset in breast cancer (6).To date, five distinct mammalian gene families for cytosolic SULTs (SULTs 1-5) have been identified (7), although SULT3 and SULT5 have not been found in humans (8). The most extensive group of the human cytosolic SULTs is the SULT1 family, which includes SULTs 1A1, 1A2, 1A3, 1B1, 1C1, 1C2, and 1E1. Each SULT has distinct substrate preferences but may also exhibit broad and overlapping substrate specificity to span the diversity of chemicals requiring sulfonation. For example, SULT1A3 catalyzes dopamine sulfonation but also accepts p-nitrophenol (pNP) with lower affinity (9, 10). SULT1A1, which shares 93% identity with SULT1A3, also sulfonates dopamine and pNP but with the reverse preference, and in addition it can sulfonate a wide range of hydrophobic molecules (Fig. 1) including xenobiotics and endogenous substrates 3,3Ј-diio...

Cytosolic sulfotransferases are believed to play a role in the neuromodulation of certain neurotransmitters and drugs. To date, four cytosolic sulfotransferases have been shown to be expressed in human brain. Recently, a novel human brain sulfotransferase has been identified and characterized, although its role and localization in the brain are unknown. Here we present the first immunohistochemical (IHC) localization of SULT4A1 in human brain using an affinity-purified polyclonal antibody raised against recombinant human SULT4A1. These results are supported and supplemented by the IHC localization of SULT4A1 in rat brain. In both human and rat brains, strong reactivity was found in several brain regions, including cerebral cortex, cerebellum, pituitary, and brainstem. Specific signal was entirely absent on sections for which preimmune serum from the corresponding animal, processed in the same way as the postimmune serum, was used in the primary screen. The findings from this study may assist in determining the physiological role of this SULT isoform.