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Domain Structure of the Glucocorticoid Receptor Protein

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Domain Structure of the Glucocorticoid Receptor Protein Proc. Nati. Acad. Sci. USA Vol. 84, pp. 4437-4440, July 1987 Biochemistry Domain structure of the glucocorticoid receptor protein (proteolysis/steroid binding/DNA binding/protein sequence) JAN CARLSTEDT-DUKE*, PER-ERIK STROMSTEDT*, ORJAN WRANGEt, TOMAS BERGMANt, JAN-AKE GuSTAFSSON*, AND HANS JORNVALLf *Department of Medical Nutrition, Karolinska Institute, Huddinge University Hospital, F69, S-141 86 Huddinge, Sweden; and Departments of tMedical Cell Genetics and tChemistry, Karolinska Institute, Box 60400, S-104 01 Stockholm, Sweden Communicated by Viktor Mutt, March 26, 1987 (receivedfor review December 1, 1986) ABSTRACT The purified rat liver glucocorticoid receptor GR was eluted with 27.5 mM MgCl2 and further purified by protein was analyzed by limited proteolysis and amino acid chromatography on DEAE-Sepharose, eluted with a linear sequence determination. The NH2 terminus appears to be NaCl gradient. The receptor was detected by analysis for 3H blocked. The steroid-binding domain, defined by a unique radioactivity. Each purification resulted in a yield of '50 ,g tryptic cleavage site, corresponds to the COOH-terminal part of GR, starting from eight rat livers. The purified prepara- of the protein with the domain border in the region of residue tions of GR contained the 94-kDa GR, the 72-kDa GR- 518. The DNA-binding domain, defined by a region with associated protein that is unrelated to GR (12, 13), as well as chymotryptic cleavage sites, is immediately adjacent to the very small amounts of proteolytic GR fragments (usually steroid-binding domain and reflects another domain border in <5% of total protein according to densitometric analysis of the region of residues 410-414. The results described at the the Coomassie blue-stained NaDodSO4/polyacrylamide gel protein level in this report confirm functional data previously following electrophoresis). obtained by mutations at the genetic level. Limited Proteolysis of GR. Purified GR was incubated with a-chymotrypsin (1 gg per ,tg of GR) or trypsin (0.3 gg per ,ug Biochemical, immunological, and genetic analyses of gluco- of GR) at 100C for 30 min. Proteins were precipitated with corticoid receptor protein (GR) imply that the protein folds 20% (wt/vol) trichloroacetic acid and analyzed by NaDod- into three distinct functional domains, which mediate hor- S04/polyacrylamide gel electrophoresis. The proteolytically mone binding (domain A), DNA binding (domain B), and an derived fragments were detected by negative staining with 1 immunodominant domain (domain C) of unknown function M KCl, cut out, and electroblotted onto glass fiber filter discs (1-7). At the protein level, these domains can be defined by (14) for direct analysis by gas-phase sequencer degradations. limited proteolysis of crude or purified preparations of rat Cleavage of GR by CNBr. Purified GR was cleaved with liver GR (2, 4, 6-8). Certain regions of the protein are highly CNBr and the resulting peptides were purified by gel- susceptible to proteolysis with a variety of proteases such as exclusion chromatography (Sephadex G-50 in 30% acetic a-chymotrypsin, trypsin, papain, or lysosomal extract. acid) and subsequent HPLC (,uBondapak C18) with a gradient These regions represent the interdomain segments and are of acetonitrile in 0.1% trifluoroacetic acid. Peptides obtained probably hinge regions within the protein. The steroid- were submitted to analysis in a sequencer. binding domain is defined by proteolysis of GR with trypsin, giving rise to a fragment with an estimated size of 27 kDa RESULTS AND DISCUSSION according to NaDodSO4/polyacrylamide gel electrophoresis (4). Digestion ofGR with a-chymotrypsin, lysosomal extract, Protein Structure. Tests for direct analysis of purified rat or very low concentrations of trypsin (7, 8) results in a liver GR (12, 13) by liquid-phase or gas-phase sequencer fragment with an estimated size of 39 kDa (4). This fragment degradations were negative, suggesting that the NH2 termi- contains both the steroid-binding and DNA-binding domains nus is blocked. This was the case for analysis of the 94-kDa (7). Further digestion of this fragment with trypsin results in GR purified by NaDodSO4/polyacrylamide gel electropho- a fragment containing only the steroid-binding domain (7). resis and for analysis of purified preparations of GR, con- Recently, cDNA clones for the human (9), rat (10), and taining both the 94-kDa GR and the 72-kDa GR-associated mouse (11) GR have been described that now enable a more protein. Different preparations ofthe receptor were therefore exact definition of the domains. In this report, we compare cleaved with trypsin, a-chymotrypsin, and cyanogen bro- the amino acid sequences of rat GR defining the functional mide. Resulting peptides were submitted to gas-phase se- domains at the protein level with the nucleotide sequences quencer analysis. Six of the CNBr fragments identified the obtained from the cDNA clone for the rat GR (10). We have NH2-terminal structures shown in Fig. 1, which are in clearly established a unique tryptic site defining the steroid- complete agreement with corresponding structures indirectly binding domain and have also strong indications of a region deduced from the cDNA nucleotide sequence for the open with chymotryptic sites defining the DNA-binding domain. reading frame (10), thus confirming the conclusions from the latter by direct analysis at six different regions. In addition, peptides from two other regions starting at positions 120 and MATERIALS AND METHODS 337 were detected but were incompletely analyzed and are Purification of GR. Rat liver GR was purified as described not included in Fig. 1, although these segments also support (12, 13). Cytosol, incubated with the synthetic glucocorticoid the indirectly deduced structure. Combined, all the se- [3H]triamcinolone acetonide, was passed through phospho- quences range from close to the NH2 terminus (residues cellulose, the receptor was activated by dilution and incuba- 28-42) to close to the COOH terminus (residues 770-790), tion at 25°C, and it was chromatographed on DNA-cellulose. inferring that the cDNA clone described (10) represents the intact receptor protein. This was further confirmed by de- The publication costs of this article were defrayed in part by page charge termination of the amino acid composition of the purified payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. Abbreviation: GR, glucocorticoid receptor protein. Downloaded by guest on October 4, 2021 4437 4438 Biochemistry: Carlstedt-Duke et al. Proc. Natl. Acad. Sci. USA 84 (1987) 200 400 600 0 0 0 0 ChTr GIQQATAGVSQDTSENPNKT 1518 II II 440 Typ 795 FIG. 1. Amino acid sequences (designated by the single-letter code) confirmed for the purified GR. GR was purified as described (11, 12) and cleaved with a-chymotrypsin (ChTr), trypsin (Tryp), or CNBr, and the resulting peptides were analyzed for amino acid sequence. The structures obtained were compared with the corresponding nucleotide sequence of rat liver GR cDNA (10). Numbers refer to the amino acid residues as defined by the nucleotide sequence for the coding region of the cDNA (total, 795 residues). Dashed arrows for the chymotryptic cleavages indicate multiple and probably nonstoichiometric cleavages, producing a less clearly defined segment than the well-defined cleavage in the case oftrypsin. Hatched region corresponds to the putative DNA-binding region (10). The sequences shown in the lower part of the figure correspond to the peptides identified after cleavage with CNBr, which cleaves after the methionine shown at the first position in each case. receptor protein after hydrolysis (Table 1) and comparison of activated GR are similar in all these respects, extensive these values with those indirectly deduced. Finally, the proteolytic processing of the protein, posttranslationally or purified activated GR has a size, as determined by electro- during activation, appears unlikely. However, limited pro- phoresis (4, 12), that is in complete agreement with that cessing occurs. Thus, as stated above, the NH2 terminus deduced from the cDNA open reading frame. Since the data appears to be blocked. From the NH2-terminal structure (10), from the cDNA and the peptide analyses for the purified the known properties ofN-acetyl-blocked proteins in general (15), and the rules for NH2-terminal processing (16), it appears likely that the mature NH2 terminus is formed by an Table 1. Amino acid composition of GR determined directly acetylated residue, which can be the initiator methionine from acid hydrolysis and compared to the composition itself. Other minor modifications cannot be completely ex- indirectly deduced from cDNA cluded, especially not in segments involving the terminal or 791-795), which were not directly demon- Hydrolysis of Indirectly from residues (1-27 cDNA clone strated by sequence analysis of the protein. purified GR, Steroid-Binding Domain. Digestion of the receptor protein mol % No. mol % with trypsin (0.3 pug per gg ofGR) yields a 27-kDa proteolytic Cys 0.6 20 2.5 fragment (Fig. 2). This fragment corresponds to the steroid- Asp I10.1 40 5.0} 9.3 binding domain, domain A (6-8). Gas-phase sequencer anal- Asn 34 4.3 ysis of this fragment after isolation by NaDodSO4/polyacryl- Thr 5.5 44 5.5 amide gel electrophoresis and electroblotting (14) shows that Ser 9.8 88 11.1 it starts with the NH2 terminus at position 518 of the intact Glu I 43 molecule. This result establishes that the fragment corre- Gln 13.8 62 51413.2 sponds to the COOH-terminal region of the protein, with the Pro 5.9 46 5.8 domain border located close to residue 518 (Fig. 1). The result Gly 8.4 57 7.2 confirms the conclusions from other results by Hollenberg Ala 6.0 42 5.3 and collaborators (9, 18), in which they have described two Val 5.1 39 4.9 different cDNA clones, of which the product of only one Met 2.3 23 2.9 binds steroids, corresponding to human GRs, OB7 and OB10.
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