Molecular characterization of two Rhesus glycoproteins from the euryhaline freshwater white-rimmed stingray, Himantura signifer, and changes in their transcript levels and protein abundance in the gills, kidney, and liver during brackish water acclimation.
Himantura signifer is a freshwater stingray which inhabits rivers in Southeast Asia. It is ammonotelic in fresh water, but retains the capacities of urea synthesis and ureosmotic osmoregulation to survive in brackish water. This study aimed to elucidate the roles of Rhesus glycoproteins (Rhgp), which are known to transport ammonia, in conserving nitrogen (N) in H. signifer during brackish water acclimation when N became limited resulting from increased hepatic urea synthesis. The complete coding sequence of rhbg from H. signifer consisted of 1383 bp, encoding 460 amino acids with an estimated molecular mass of 50.5 kDa, while that of rhcg comprised 1395 bp, encoding for 464 amino acids with an estimated molecular mass of 50.8 kDa. The deduced amino sequences of Rhbg and Rhcg contained ammonia binding sites, which could recruit NH4+to be deprotonated, and a hydrophobic pore with two histidine residues, which could mediate the transport of NH3. Our results indicated for the first time that brackish water acclimation resulted in significant decreases in the expression levels of rhbg/Rhbg and rhcg/Rhcg in the gills of H. signifer, which offered a mechanistic explanation of brackish water-related decreased ammonia excretion reported elsewhere. Furthermore, rhbg/Rhbg expression levels increased significantly in the liver of H. signifer during brackish water acclimation, indicating that the ammonia produced by extra-hepatic tissues and released into the blood could be channeled into the liver for increased urea synthesis. Overall, these results lend support to the proposition that H. signifer becomes N-limited upon utilizing urea as an osmolyte in brackish water.
Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Singapore.
Cheng T
CT
Yeam
Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Singapore.
You R
YR
Chng
Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Singapore.
Jasmine L Y
JLY
Ong
Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Singapore.
Wai P
WP
Wong
Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore, 637616, Singapore.
Shit F
SF
Chew
Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore, 117543, Singapore. dbsipyk@nus.edu.sg.|The Tropical Marine Science Institute, National University of Singapore, Kent Ridge, Singapore, 119227, Singapore. dbsipyk@nus.edu.sg.
Yuen K
YK
Ip
D000641:Ammonia / Q000378:metabolism; D000818:Animals; D003001:Cloning, Molecular; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005618:Fresh Water / Q000737:chemistry*; D005786:Gene Expression Regulation; D005880:Gills / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D064587:Osmoregulation; D011487:Protein Conformation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012204:Rh-Hr Blood-Group System / Q000235:genetics / Q000378:metabolism*; D000068357:Saline Waters / Q000737:chemistry*; D054712:Salinity; D055049:Salt Tolerance; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D012860:Skates, Fish / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014158:Transcription, Genetic; D014508:Urea / Q000378:metabolism
D029941:Fish Proteins; D006023:Glycoproteins; D012333:RNA, Messenger; D012204:Rh-Hr Blood-Group System; D000641:Ammonia; D014508:Urea
Ammonia; Elasmobranchs; Osmoregulation; Salinity adaptation; Urea; Ureosmotic