Disease relevance of nec

• Nec was expressed in Escherichia coli, and the purified protein folded to the active native conformation required for protease inhibitory activity [1].
• In addition, we identify two nec mutations homologous to an antithrombin point mutation that is responsible for neonatal thrombosis [2].
• These necrotic mutations are temperature sensitive, which is in keeping with the temperature-dependent polymerization of serpins in vitro and the role of childhood fevers in exacerbating liver disease in Z alpha-antitrypsin deficiency [2].

High impact information on nec

• Spaetzle was cleaved by proteolytic enzymes to its active ligand form shortly after immune challenge, and cleaved Spaetzle was constitutively present in Spn43Ac-deficient flies [3].
• Hence, Spn43Ac negatively regulates the Toll signaling pathway, and Toll does not function as a pattern recognition receptor in the Drosophila host defense [3].
• Drosophila mojavensis adults, which breed and feed on necrotic cacti, show an increase in longevity when exposed to atmospheric ethanol [4].
• The validity of the fruit-fly as a model of human disease has been confirmed in a striking way by Green and colleagues.1 They show that the mutations causing a necrotic disease phenotype in Drosophila, precisely mirror those resulting in a group of well-studied but perplexing diseases in the human [5].
• Transgenic flies carrying an S>F amino-acid substitution equivalent to that found in Siiyama-variant antitrypsin (nec(S>F.UAS)) fail to complement nec-null mutations and demonstrate a dominant temperature-dependent inactivation of the wild-type nec allele [2].

Biological context of nec

• The TOLL-mediated immune response to fungal infections is constitutively activated in nec mutants and pleiotropic phenotypes include melanization and cellular necrosis [6].
• The nec gene corresponds to Spn43Ac, one of a cluster of three putative serine proteinase inhibitors at 43A1.2, on the right arm of chromosome 2 [6].
• Small stress protein expression enhances the survival of mammalian cells exposed to numerous injuries that induce necrotic cell death [7].
• Cells suffer necrotic death when exposed to extreme environmental conditions, adverse and excessive stimuli, or when deleterious mutations are encoded in their genetic material [8].
• Mutant germ cells do not undergo programmed cell death, but instead undergo a necrotic-type death, and their general poor health apparently prevents surviving germ cells from forming gametes [9].

Anatomical context of nec

• These phenotypes include neural degeneration in the eye and in the optic lobe of the adult brain that begins 60 hr after pupariation and produces a dark, necrotic eye spot in the adult eye [10].
• During early limb development Dlx-5 is also expressed in the mesoderm at the anterior margin of the limb bud and in a discrete group of mesodermal cells at the mid-proximal posterior margin that corresponds to the posterior necrotic zone [11].

Associations of nec with chemical compounds

• We show that necrotic mutations that are identical to the Z-deficiency variant of alpha(1)-antitrypsin form urea-stable polymers in vivo [2].
• Necrotic carries a polyglutamine extension amino-terminal to the core serpin structure [12].
• Acridine orange appears to selectively stain apoptotic forms of death in these preparations, since cells undergoing necrotic deaths were not significantly labelled [13].
• The lysine to glutamine substitutions had no effect on the overall structure of recombinant Necrotic protein but abolished the formation of stable complexes with target proteases [14].
• Necrotic contains three basic lysine residues within the D-helix that are homologous to those found in the heparin-binding domain of antithrombin and heparin co-factor II [14].

Regulatory relationships of nec

• These data show that Necrotic is likely to inhibit a wide range of proteases in Drosophila and that Nec has the specificity requirements to act as the physiological inhibitor of Persephone in vivo [1].

Other interactions of nec

• This finding indicates that cleavage of the Necrotic amino-terminal extension might modulate Toll activation following the initial immune response [12].
• The necrotic gene in Drosophila corresponds to one of a cluster of three serpin transcripts mapping at 43A1.2 [6].
• The Msx-1 transcripts were found in the limb mesenchymal cells in the region covering the necrotic zone and ectodermal cells overlying such mesenchymal cells [15].
• Despite the homology to other serpins, Necrotic did not bind, nor was it activated by sulfated glycans [14].
• Several species of columnar cacti in the Sonoran Desert contain isoquinoline alkaloids that are toxic to all but the resident drosophilids that feed and breed in necrotic stems [16].

References