Bombyx mori, amino acid sequence

Fig. 6 Sequence alignment of the deduced amino acid sequence from the identified cDNA encoding PBAN and related peptides from Helicoverpa zea and Bombyx mori. The putatively expressed peptides are shown in boxes. The conserved amino acids are underlined in the B. mori sequence. Putative proteolytic posttranslational processing sites are shown in bold with glycine contributing the C-terminal amide. Sequences of PBAN-like peptides are also shown in Table 1. GenBank accession numbers H. zea - PI 1159 and B. mori - BAA05971...

In moths, it was discovered in Helicoverpa zea that a peptide produced in the subesophageal ganglion portion of the brain complex regulates pheromone production in female moths (19). This factor has been purified and characterized in three species, Helicoverpa zea (20), Bombyx mori (21, 22), and Lymantria dispar (23). They are all a 33- or 34-amino acid peptide (named pheromone biosynthesis activating neuropeptide, PBAN) and have in common an amidated C-terminal 5-amino acid sequence (FXPRL-amide), which is the minimum peptide fragment required for pheromon-tropic activity. In the redbanded leafroller moth, it was shown that PBAN from the brain stimulates the release of a different peptide from the bursae copulatrix that is used to stimulate pheromone production in the pheromone gland found at the posterior tip of the abdomen (24). 

Ha, S. W., Gracz, H. S., Tonelli, A. E., and Hudson, S. M. (2005). Structural study of irregular amino acid sequences in the heavy chain of Bombyx mori silk fibroin. Biomacromolecules 6, 2563-2569. 

Silk is produced from the spun threads from silkworms (the larvae of the moth Bombyx mori and related species). The main protein in silk, fibroin, consists of antiparallel pleated sheet structures arranged one on top of the other in numerous layers (1). Since the amino acid side chains in pleated sheets point either straight up or straight down (see p. 68), only compact side chains fit between the layers. In fact, more than 80% of fibroin consists of glycine, alanine, and serine, the three amino acids with the shortest side chains. A typical repetitive amino acid sequence is (Gly-Ala-Gly-Ala-Gly-Ser). The individual pleated sheet layers in fibroin are found to lie alternately 0.35 nm and 0.57 nm apart. In the first case, only glycine residues (R = H) are opposed to one another. The slightly greater distance of 0.57 nm results from repulsion forces between the side chains of alanine and serine residues (2). 

Kitamura A., Nagasawa H., Kataoka H., Inoue T., Matsumoto S., Ando T. and Suzuki A. (1989) Amino acid sequence of pheromone biosynthesis activating neuropeptide (PB AN) of the silkworm, Bombyx mori. Biochem. Biophys. Res. Commun. 163, 520-526. 

Amino acid sequence of pheromone-biosynthesis-activating neuropeptide (PB AN) of the silkworm, Bombyx mori. Biochem. Biophys. Res. Commun. 163, 520-526. 

Prothoracicotropic hormone (Bombyx PTTH) of the silkworm, Bombyx mori, was extracted from adult heads. Bombyx PTTH is suggested to be a glyco-peptide and consists of two essentially identical subunits. Amino acid sequencing and cDNA analysis revealed the whole amino acid sequence of the subunit, composed of 104-109 residues. Bombyx PTTH stimulated adult development in brainless Bombyx pupae at a dose of ca. 0.1 ng and also enhanced the release of ecdysone in vitro at a concentration of 10 M. Immunohistochemistry and in situ hybridization showed that Bombyx PTTH was transcribed and translated in two pairs of dorso-lateral neurosecretory cells in the brain. 

Figure 1. Amino acid sequences of PBAN from Helicoverpa zea (Hez-PBAN) top, and Bombyx mori (Bom-PBAN) bottom. Amino acids in Bom-PBAN sequence shown in bold letters indicate differences in primary structure compared to Hez-PBAN.

Amino acid composition MA, MI, FLAG, and CYL from Dicko et al. (2004b), Acinous and Pyriform from unpublished data, Bombyx mori, Antheraea pemyi, and Galleria mellonella from sequences. 

Bombyx mori silk has both crystalline and amorphous domains. In the crystalline fraction, there is a high proportion of glycine (Gly), alanine (Ala) and serine (Ser) amino acid residues, present in the ratio of 3 2 1. This reflects the presence of hexapep-tide sequences, Gly-Ala-Gly-Ala-Gly-Ser. You ve probably forgot the structure of these amino acids, which we have therefore reproduced in Figure 9-16. 

In each separate thread there are 10-nm-wide microfibrils bound into fibrillary bands of up to 2 000 nm in width. The protein chains are present in the microfibrils as folded chains. These so-called silk fibroins can be separated with chymotrypsin into an X-ray crystalline (60% by wt) and an amorphous part. The crystalline portion consists of uniform hexapeptide units (-ser-gly-ala-gly-ala-gly-). In fibroins from Bombyx mori L. there are ten of these hexapeptides. The 60 a-amino acid residues of the crystalline part are joined together with 33 amino acid units of the amorphous component in one peptide chain. The amino acids of the amorphous part vary widely in composition and sequence length. 

All silks are not, however, chemically identical. Different silkworm species produce fibrous proteins that contain different sequences and proportions of amino acids. These compositional differences in turn influence the mechanical properties of the fibers. The most common form of sUk, produced by the silkworm Bombyx mori from which most silk sutures are made, has a predominant six-residue sequence Gly-Ser-Gly-Ala-Gly-Ala, which repeats itself for long distances along the chain. This sequence accounts for a large proportion of the amino acid residues that are present. 

The silks of insects like the silkworm Bombyx mori have been mentioned several times in this chapter in fact, far more is known about the biochemistry, molecular biology and genetics of the silkworm than of any spider. There are many similarities between insect silks and spider silks, e.g. the predominance of amino acids with short side chains or the occurrence of some sequence motifs, which can help to understand the general principles involved in the generation of their material properties. Yet, there are also major differences that have to be taken into account. Most insect silks are used as cocoons or protective webs in larval stages and originate in labial glands [32]. In contrast. 

Silk fibers from the Bombyx mori silkworm have a 5-10 micron sized triangular cross section. The fibroin-rich chain is composed mostly of beta-sheets, due to a 59-mer amino acid repeat sequence. Silkworm fibers are extmded from two silkworm glands as a pair of primary filaments (brin) that are stuck together with sericin proteins acting like glue. Silk is one of the strongest natural fibers but loses up to 20% of its strength when wet. 

Silks are fibrous protein, some forms of which can be woven into textiles. The best known type of silk have a range of functions, including cocoons of the larvae of the mulberry silkworm. Bombyx mori are reared in captivity [41, 143, 145]. They have repetitive protein sequence [29] with a predominance of alanine, glycine and serine (which is high in silkworm silks but low in spider silks). Silk proteins are comprised of four different structural components (1) elastic [3-spirals, (2) crystalline P-sheets rich in alanine, (3) tight amino acid repeats forming a-helices, and (4) spacer regions [47, 126]. 

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