Biology subjects

Hirayama, C.

Publications and source records attributed to Hirayama, C..

4 recordsLinked to original sources

bioRxiv2025

An ATP-binding cassette subfamily C is crucial for flavonoid sequestration in the domestic silkworm, Bombyx mori

Some herbivorous insects have evolved sequestration mechanisms, the ability to take up and accumulate plant secondary metabolites for their own benefit. The domestic silkworm, Bombyx mori, and its wild ancestor, B. mandarina, take up flavonoids from mulberry leaves and accumulate the molecules as their glucosides in their tissues and cocoon shell. This sequestration enhances the cocoons protective property against ultraviolet or bacterial proliferation. Here, we show that an ATP-binding cassette transporter subfamily C (ABCC) gene, BmABCC4, plays a crucial role in the flavonoid sequestration in the silkworms. BmABCC4 is located at Green c, a cocoon color-associated locus predicted in 1941 and whose detailed position we previously identified. This transporter is expressed in the midgut and silk glands, and the expression is upregulated in the midgut in late period of final instar larva. Knockout of BmABCC4 significantly reduced the total flavonoid content in the tissues and cocoon shell. Our results suggest that BmABCC4 transports flavonoid glucosides from the midgut cells to hemolymph and from the silk gland cells to the silk gland lumen.

genetics↗

bioRxiv2023

A major endogenous glycosidase mediating quercetin uptake in Bombyx mori

Quercetin is a common plant flavonoid that is involved in herbivore-plant interactions. Mulberry silkworms (domestic silkworm, Bombyx mori, and wild silkworm, Bombyx mandarina) uptake quercetin from mulberry leaves and accumulate the metabolites in the cocoon, thereby improving its protective properties. Here we identified and characterized a glycosidase, named LPH-like quercetin glycoside hydrolase 1 (LQGH1), that initiates quercetin metabolism in the domestic silkworm. LQGH1 is expressed in the midgut where it mediates quercetin uptake by deglycosylating the three most common quercetin glycosides present in mulberry leaf: rutin, quercetin-3-O-malonyl-glucoside, quercetin-3-O-glucoside. Despite being located in an unequal crossing-over hotspot, LQGH1 is conserved in some species in clade Macroheterocera, including the wild silkworm, indicating the adaptive significance of quercetin uptake. LQGH1 is important also in breeding: defective mutations of LQGH1, which result in discoloration of the cocoon and increased silk yield, are homozygously conserved in 27 of the 32 Japanese white-cocoon domestic silkworm strains and 12 of the 30 Chinese ones we investigated.

genetics↗

bioRxiv2021

Distinct roles and actions of PDI family enzymes in catalysis of nascent-chain disulfide formation

The mammalian endoplasmic reticulum (ER) harbors more than 20 members of the protein disulfide isomerase (PDI) family that act to maintain proteostasis. Herein, we developed an in vitro system for directly monitoring PDI- or ERp46-catalyzed disulfide bond formation in ribosome-associated nascent chains (RNC) of human serum albumin. The results indicated that ERp46 more efficiently introduced disulfide bonds into nascent chains with short segments exposed outside the ribosome exit site than PDI. Single-molecule analysis by high-speed atomic force microscopy further revealed that PDI binds nascent chains persistently, forming a stable face-to-face homodimer, whereas ERp46 binds for a shorter time in monomeric form, indicating their different mechanisms for substrate recognition and disulfide bond introduction. Similarly to ERp46, a PDI mutant with an occluded substrate-binding pocket displayed shorter-time RNC binding and higher efficiency in disulfide introduction than wild-type PDI. Altogether, ERp46 serves as a more potent disulfide introducer especially during the early stages of translation, whereas PDI can catalyze disulfide formation in RNC when longer nascent chains emerge out from ribosome.

biochemistry↗

bioRxiv2020

A unique adhesive motif of protein disulfide isomerase P5 supports its function via dimerization

P5, also known as PDIA6, is a PDI-family member that plays an important role in the ER quality control. Herein, we revealed that P5 dimerizes via a unique adhesive motif contained in the N-terminal thioredoxin-like domain. This motif is apparently similar to, but radically different from conventional leucine-zipper motifs, in that the former includes a periodic repeat of leucine or valine residues at the third or fourth position spanning five helical turns on 15-residue anti-parallel -helices, unlike the latter of which the leucine residues appear every two helical turns on [~]30-residue parallel -helices at dimer interfaces. A monomeric P5 mutant with the impaired adhesive motif showed structural instability and local unfolding, and behaved as an aberrant protein that induces the ER stress response. Disassembly of P5 to monomers compromised its ability to inactivate IRE1 via reduction of intermolecular disulfide bonds and its Ca2+-dependent regulation of chaperone function in vitro. Thus, the leucine-valine adhesive motif supports structure and physiological function of P5.

biochemistry↗