Structure of a novel farnesylated bilin from an insect - formation by α-cleavage of heme A of mitochondrial cytochrome coxidases?

Farnesyl biliverdins IXα are novel ligands of biliproteins from moths of the Noctuoidea superfamily: A chemosystematic view of the Lepidoptera

Bilins, derived from biliverdin IXα, are known from animals, plants and microorganisms, where they play vital roles as light-absorbing pigments. Bilins occur also in many insects. Recently, we discovered in insects a novel structural type of bilins with a farnesyl substituent at pyrrole ring A of biliverdin IXα. The first of these unusual bilins with a molecular mass of 852 (C₄₈H₆₀O₁₀N₄) was identified in Cerura vinula, subsequently in Spodoptera littoralis; both species are members of the Noctuoidea superfamily of moths. From an evolutionary point of view, it was of interest to examine other species and families of this monophyletic clade. Here, we show that other moths species in this clade (three Notodontidae species, one Erebidae species, and one Noctuidae species) have farnesylated biliverdins IXα that are present as a mixture of three bilins, differing by the number of oxygen atoms (O_8-10). These bilins are associated with typical hemolymph storage proteins, which were identified by mass spectroscopic sequencing of tryptic peptides as arylphorins (a class of 500-kDa hexamerins) in the Notodontidae and Erebidae families, and as 350-kDa very high-density lipoproteins in the Noctuidae family. Circular dichroism spectroscopy revealed that the bilins adopt opposite conformations in complex with the two different classes of proteins. At present, farnesylated biliverdins and IXα-isomers of bilins in general are known only from species of the Noctuoidea clade; the sister clades of Bombycoidea and Papilionoidea synthesise the IXγ-isomer of biliverdin and derivatives thereof.

Heme Oxygenases in Cardiovascular Health and Disease

Heme oxygenases are composed of two isozymes, Hmox1 and Hmox2, that catalyze the degradation of heme to carbon monoxide (CO), ferrous iron, and biliverdin, the latter of which is subsequently converted to bilirubin. While initially considered to be waste products, CO and biliverdin/bilirubin have been shown over the last 20 years to modulate key cellular processes, such as inflammation, cell proliferation, and apoptosis, as well as antioxidant defense. This shift in paradigm has led to the importance of heme oxygenases and their products in cell physiology now being well accepted. The identification of the two human cases thus far of heme oxygenase deficiency and the generation of mice deficient in Hmox1 or Hmox2 have reiterated a role for these enzymes in both normal cell function and disease pathogenesis, especially in the context of cardiovascular disease. This review covers the current knowledge on the function of both Hmox1 and Hmox2 at both a cellular and tissue level in the cardiovascular system. Initially, the roles of heme oxygenases in vascular health and the regulation of processes central to vascular diseases are outlined, followed by an evaluation of the role(s) of Hmox1 and Hmox2 in various diseases such as atherosclerosis, intimal hyperplasia, myocardial infarction, and angiogenesis. Finally, the therapeutic potential of heme oxygenases and their products are examined in a cardiovascular disease context, with a focus on how the knowledge we have gained on these enzymes may be capitalized in future clinical studies.

Very high-density lipoprotein and vitellin as carriers of novel biliverdins IXα with a farnesyl side-chain presumably derived from heme A in Spodoptera littoralis

Bilins in complex with specific proteins play key roles in many forms of life. Biliproteins have also been isolated from insects; however, structural details are rare and possible functions largely unknown. Recently, we identified a high-molecular weight biliprotein from a moth, Cerura vinula, as an arylphorin-type hexameric storage protein linked to a novel farnesyl biliverdin IXα; its unusual structure suggests formation by cleavage of mitochondrial heme A. In the present study of another moth, Spodoptera littoralis, we isolated two different biliproteins. These proteins were identified as a very high-density lipoprotein (VHDL) and as vitellin, respectively, by mass spectrometric sequencing. Both proteins are associated with three different farnesyl biliverdins IXα: the one bilin isolated from C. vinula and two new structurally closely related bilins, supposed to be intermediates of heme A degradation. The different bilin composition of the two biliproteins suggests that the presumed oxidations at the farnesyl side-chain take place mainly during egg development. The egg bilins are supposedly transferred from hemolymph VHDL to vitellin in the female. Both biliproteins show strong induced circular dichroism activity compatible with a predominance of the M-conformation of the bilins. This conformation is opposite to that of the arylphorin-type biliprotein from C. vinula. Electron microscopy of the VHDL-type biliprotein from S. littoralis provided a preliminary view of its structure as a homodimer and confirmed the biochemically determined molecular mass of ∼350 kDa. Further, images of S. littoralis hexamerins revealed a 2 × 3 construction identical to that known from the hexamerin from C. vinula.