Elsevier BV Acta Medica Okayama 1096-4959 281 2026 N-terminal domains and site-specific glycosylation regulate the secretion of avian melanocortin inverse agonists, agouti signaling protein (ASIP) and agouti-related protein (AGRP) 111174 EN Hibiki Fukuchi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Ryoya Watanabe Graduate School of Natural Science and Technology, Okayama University Yuna Iida Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Saya Nakano Graduate School of Natural Science and Technology, Okayama University Aya Mizutani Graduate School of Natural Science and Technology, Okayama University Tatsuhiko Abo Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Sayaka Aizawa Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Sakae Takeuchi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Agouti signaling protein (ASIP) and agouti-related protein (AGRP) are paralogous inverse agonists of melanocortin receptors with distinct physiological roles, but their structural and biochemical properties in birds remain poorly understood. Here, we characterized chicken ASIP and AGRP proteins. Analysis of available sequences revealed that a motif resembling the mammalian proprotein convertase 1/3 (PC1/3, also known as PCSK1) cleavage site is conserved across a broad range of avian orders, but Western blot analysis of transfected Chinese hamster ovary (CHO-K1) cells and chicken hypothalamus detected no cleavage, suggesting that avian AGRP may not be post-translationally processed at this site. Chicken ASIP mRNA contains an in-frame upstream ATG (uATG) and a putative N-linked glycosylation site at Asn-42, both conserved across multiple avian orders. Overexpression in CHO-K1 cells showed that ASIP translated from either ATG produces a mature protein of the same size that is N-glycosylated at Asn-42 and exhibits markedly lower secretion efficiency than AGRP. Domain-swapping experiments revealed that the N-terminal domain reduces secretion, whereas a naturally occurring ASIP-b variant with an additional N-glycan at Asn-47 shows enhanced secretion. Proteasome inhibition increased intracellular ASIP, and endoglycosidase H (Endo H) sensitivity indicated endoplasmic reticulum (ER) retention, suggesting that the N-terminal domain limits secretion via ER-associated proteasomal degradation. These findings reveal species-specific post-translational regulation of avian melanocortin inverse agonists, in which N-terminal features and site-specific N-glycosylation determine secretion efficiency, likely contributing to their distinct roles in pigmentation and hypothalamic energy balance. No potential conflict of interest relevant to this article was reported.

The Genetics Society of Japan Acta Medica Okayama 1341-7568 95 3 2020 Ribosome rescue activity of an Arabidopsis thaliana ArfB homolog 119 131 EN Michiaki Nagao Graduate School of Natural Science and Technology, Okayama University Fumina Tsuchiya Graduate School of Integrated Science and Technology, Shizuoka University Reiko Motohashi Graduate School of Integrated Science and Technology, Shizuoka University Tatsuhiko Abo Graduate School of Natural Science and Technology, Okayama University A homolog of the bacterial ribosome rescue factor ArfB was identified in Arabidopsis thaliana. The factor, named AtArfB for Arabidopsis thaliana ArfB, showed ribosome rescue activity in both in vivo and in vitro assays based on the bacterial translation system. As has been shown for ArfB, the ribosome rescue activity of AtArfB was dependent on the GGQ motif, the crucial motif for the function of class I release factors and ArfB. The C-terminal region of AtArfB was also important for its function. The N-terminal region of AtArfB, which is absent in bacterial ArfB, functioned as a transit peptide for chloroplast targeting in tobacco cells. These results strongly suggest that AtArfB is a ribosome rescue factor that functions in chloroplasts. No potential conflict of interest relevant to this article was reported.