The amino acid sequence of neuropolypeptide h3 from Homo sapiens brain has been determined. It revealed that h3 is the exact counterpart of the 21-kDa protein from Bos taurus brain and the 23-kDa protein from Rattus norvegicus brain: The three proteins belong to the same 21-23-kDa protein family. Multiple tissue Northern blots showed that the mRNA encoding the 21-23-kDa protein is expressed in different amounts according to tissues and species; it is particularly abundant in Rattus norvegicus testis.
A cytosolic 21-kDa protein isolated from bovine brain was demonstrated to bind hydrophobic ligands, particularly phosphatidylethanolamine. It was encountered in several tissues and species ; however, its accurate function remained partially unknown. In order to obtain information from its structural features, we built a molecular model which revealed it to possess a nucleotide-binding site. In the present research, we describe the affinity of the bovine brain 21-kDa protein for nucleotides, and its association with cytosolic proteins, small GTP-binding proteins and lipid droplets. Our results suggest that, through its association with small GTP-binding proteins, the 21 -kDa protein is implicated in signal mechanisms during cell growth and maturation.From bovine brain, Bernier and Jolli% purified, in 1984, a soluble basic 23-kDa protein which showed a significant affinity for organic anions [l]. The protein was further characterized as a phosphatidylethanolamine-binding protein, suggesting its involvement in lipid metabolism [2]. The determination of its complete amino acid sequence 131 revealed the correct molecular mass to be 21-kDa. The comparison of the primary structure of the 21-kDa protein with sequence protein data banks showed very few significant sequence similarities; it was concluded that, from a structural point of view, the 21-kDa protein might represent a new type of protein [3]. Immunochemical studies using a rabbit antiserum demonstrated the presence of the 21-kDa protein in the entire cytoplasm, along the plasma membrane and the membranes of rough endoplasmic reticulum in rat brain oligodendrocytes Independent of these experiments, Bollengier and Mahler purified, in 1980, a cytosolic protein from human brain, identified as h3 [5]. In SDSPAGE, the human h3 behaved as a protein of molecular mass approximately 23 kDa. Further physicochemical studies showed that the human brain protein h3 possessed two free sulphydryl groups responsible for doublet (21 kDa and 23 kDa) and polymer formation by disulphide bonding [6]. Immunoblotting revealed the presence of protein h3 in different tissues from human, bovine, rat and chicken species 171. Recently, the human protein h3 primary structure was established both by deduction from the corresponding cDNA sequence and by direct microsequencing of the purified protein [8]; it was shown to be constituted by 186 amino acids corresponding to a calculated molecular mass of 21 kDa and present 95% sequence identity with the bovine 21-kDa protein. Furthermore, by morphine affinity chromatography, Grandy et al. 191 isolated a 23-kDa protein from rat brain membranes; although not an opioid receptor itself, the rat brain 23-kDa protein may be associated with such a receptor. The authors screened a rat brain cDNA library and established the sequence of a cDNA coding for the 23-kDa rat brain protein. The deduced 23-kDa protein shared 85% identity with the bovine 21-kDa protein and 85.5% identity with the human protein h3, revealing that the three mammalian proteins are mem...
A 21 kDa protein purified from bovine brain cytosol was previously described as a hydrophobic ligand binding protein; however, its accurate biological function remained still uncertain. In order to get further information about its potential biological role, an extended prediction of its secondary and three dimensional structures was undertaken. We describe here a process which permitted us to discover a structural homology between the 21 kDa protein and the N-domain of yeast phosphoglycerate kinase (PGK). This process is based on comparing the 21 kDa protein with all the proteins presenting a slight homology, by using the Hydrophobic Cluster Analysis (HCA) method. According to the observed similarity between the N-domain of yeast PGK and the 21 kDa protein, we built a model which was shown to possess a potential binding site for nucleotides. Moreover, the model obtained presents three-dimensional (3D) structure similarity with adenylate kinase. These results suggest two main hypotheses: (i) the 21 kDa protein may belong to the kinase family; (ii) the binding of a nucleotide could imply a modification of the 3D structure of the 21 kDa protein that can promote the transfer of hydrophobic ligands to the plasma membrane. Meanwhile, verification of these hypotheses has been in part performed experimentally: the 21 kDa protein binds MgATP as well as, to a lesser extent, phosphoglycerate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.