首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Rme1p is a zinc-finger protein and has a pivotal role in control of meiosis in Saccharomyces cerevisiae. The DNA binding domain of Rme1p consists of three zinc-finger segments and the C-terminal 16 amino acid residues (called C-TR). To examine the role of C-TR, a series of mutant Rme1p fused with maltose binding protein (MBP) were constructed, purified, and characterized, in terms of the DNA binding ability. The basic amino acid residues R287 and K290, and the hydrophobic residues F288, L292, 1295, and L296 play an important role for DNA binding, suggesting that the C-TR forms an amphipathic alpha-helix. Also, it was shown that the mutations in the basic amino acid residues abolish the repression and inhibition of spore formation by Rme1p in vivo. Hence, the C-TR is important for in vivo function of Rme1p.  相似文献   

3.
4.
Stat3 is activated by cytokines and growth factors via specific tyrosine phosphorylation, dimerization, and nuclear translocation. However, the mechanism involved in its nuclear translocation is unclear. In this study, by systematic deletion and site-directed mutagenesis we identified Arg-214/215 in the alpha-helix 2 region of the coiled-coil domain of Stat3 as a novel sequence element essential for its nuclear translocation, stimulated by epidermal growth factor as well as by interleukin-6. Furthermore, we identified Arg-414/417 in the DNA binding domain as also required for the nuclear localization of Stat3. This sequence element corresponds to Lys-410/413 of Stat1, a reported sequence for Stat1 nuclear translocation. On the other hand, Leu-411 of Stat3, corresponding to Leu-407 of Stat1, a necessary residue for Stat1 nuclear transport, is not essential for Stat3 nuclear import. The mutant of Arg-214/215 or Arg-414/417 was shown to be tyrosyl-phosphorylated normally but failed to enter the nucleus in response to epidermal growth factor or interleukin-6. The defect, however, can be rescued by the wild-type Stat3 but cannot be compensated by these two mutants. Mutations on Arg-414/417, but not Arg-214/215, destroy the DNA binding activity of Stat3. Our data for the first time identified a sequence element located in the coiled-coil domain that is involved in the ligand-induced nuclear translocation of Stat3. This novel sequence together with a conserved sequence element in the DNA binding domain coordinates to mediate the nuclear translocation of Stat3.  相似文献   

5.
Saccharomyces cerevisiae Cet1p is the prototype of a family of metal-dependent RNA 5'-triphosphatases/NTPases encoded by fungi and DNA viruses; the family is defined by conserved sequence motifs A, B, and C. We tested the effects of 12 alanine substitutions and 16 conservative modifications at 18 positions of the motifs. Eight residues were identified as important for triphosphatase activity. These were Glu-305, Glu-307, and Phe-310 in motif A (IELEMKF); Arg-454 and Lys-456 in motif B (RTK); Glu-492, Glu-494, and Glu-496 in motif C (EVELE). Four acidic residues, Glu-305, Glu-307, Glu-494, and Glu-496, may comprise the metal-binding site(s), insofar as their replacement by glutamine inactivated Cet1p. E492Q retained triphosphatase activity. Basic residues Arg-454 and Lys-456 in motif B are implicated in binding to the 5'-triphosphate. Changing Arg-454 to alanine or glutamine resulted in a 30-fold increase in the K(m) for ATP, whereas substitution with lysine increased K(m) 6-fold. Changing Lys-456 to alanine or glutamine increased K(m) an order of magnitude; ATP binding was restored when arginine was introduced. Alanine in lieu of Phe-310 inactivated Cet1p, whereas Tyr or Leu restored function. Alanine mutations at aliphatic residues Leu-306, Val-493, and Leu-495 resulted in thermal instability in vivo and in vitro. A second S. cerevisiae RNA triphosphatase/NTPase (named Cth1p) containing motifs A, B, and C was identified and characterized. Cth1p activity was abolished by E87A and E89A mutations in motif A. Cth1p is nonessential for yeast growth and, by itself, cannot fulfill the essential role played by Cet1p in vivo. Yet, fusion of Cth1p in cis to the guanylyltransferase domain of mammalian capping enzyme allowed Cth1p to complement growth of cet1Delta yeast cells. This finding illustrates that mammalian guanylyltransferase can be used as a vehicle to deliver enzymes to nascent pre-mRNAs in vivo, most likely through its binding to the phosphorylated CTD of RNA polymerase II.  相似文献   

6.
7.
Site-directed mutagenesis was performed on several areas of MutH based on the similarity of MutH and PvuII structural models. The aims were to identify DNA-binding residues; to determine whether MutH has the same mechanism for DNA binding and catalysis as PvuII; and to localize the residues responsible for MutH stimulation by MutL. No DNA-binding residues were identified in the two flexible loop regions of MutH, although similar loops in PvuII are involved in DNA binding. Two histidines in MutH are in a similar position as two histidines (His-84 and His-85) in PvuII that signal for DNA binding and catalysis. These MutH histidines (His-112 and His-115) were changed to alanines, but the mutant proteins had wild-type activity both in vivo and in vitro. The results indicate that the MutH signal for DNA binding and catalysis remains unknown. Instead, a lysine residue (Lys-48) was found in the first flexible loop that functions in catalysis together with the three presumed catalytic amino acids (Asp-70, Glu-77, and Lys-79). Two deletion mutations (MutHDelta224 and MutHDelta214) in the C-terminal end of the protein, localized the MutL stimulation region to five amino acids (Ala-220, Leu-221, Leu-222, Ala-223, and Arg-224).  相似文献   

8.
Cyclophilin 40 (CyP40) is a tetratricopeptide repeat (TPR)-containing immunophilin and a modulator of steroid receptor function through its binding to heat shock protein 90 (Hsp90). Critical to this binding are the carboxyl-terminal MEEVD motif of Hsp90 and the TPR domain of CyP40. Two different models of the CyP40-MEEVD peptide interaction were used as the basis for a comprehensive mutational analysis of the Hsp90-interacting domain of CyP40. Using a carboxyl-terminal CyP40 construct as template, 24 amino acids from the TPR and flanking acidic and basic domains were individually mutated by site-directed mutagenesis, and the mutants were coexpressed in yeast with a carboxyl-terminal Hsp90beta construct and qualitatively assessed for binding using a beta-galactosidase filter assay. For quantitative assessment, mutants were expressed as glutathione S-transferase fusion proteins and assayed for binding to carboxyl-terminal Hsp90beta using conventional pulldown and enzyme-linked immunosorbent assay microtiter plate assays. Collectively, the models predict that the following TPR residues help define a binding groove for the MEEVD peptide: Lys-227, Asn-231, Phe-234, Ser-274, Asn-278, Lys-308, and Arg-312. Mutational analysis identified five of these residues (Lys-227, Asn-231, Asn-278, Lys-308, and Arg-312) as essential for Hsp90 binding. The other two residues (Phe-234 and Ser-274) and another three TPR domain residues not definitively associated with the binding groove (Leu-284, Lys-285, and Asp-329) are required for efficient Hsp90 binding. These data confirm the critical importance of the MEEVD binding groove in CyP40 for Hsp90 recognition and reveal that additional charged and hydrophobic residues within the CyP40 TPR domain are required for Hsp90 binding.  相似文献   

9.
10.
11.
The zinc finger protein Rme1p is a negative regulator of the meiotic activator IME1 in Saccharomyces cerevisiae . Prior studies have shown that Rme1p binds in vitro to a site near nt -2030 in the IME1 upstream region, but a genomic mutation in that site has little effect on repression of IME1 . To identify Rme1p binding sites in vivo , we have examined the binding of Rme1p to genomic sites through in vivo footprinting. We show that Rme1p binds to two sites in the IME1 upstream region, near nt -1950 and -2030. Mutations in both binding sites abolish repression of chromosomal IME1 by Rme1p, whereas a mutation in either single site causes partial derepression. Therefore, both Rme1p binding sites are essential for repression of IME1 . Prior studies have shown that repression by Rme1p depends upon RGR1 and SIN4 , which specify RNA polymerase II mediator subunits that are required for normal nucleosome density. We find that RGR1 and SIN4 are not simply required for Rme1p to bind to DNA in vivo . These results suggest that Rme1p functions directly as a repressor of IME1 and that Rgr1p and Sin4p are required for DNA-bound Rme1p to exert repression.  相似文献   

12.
13.
An hereditary abnormal antithrombin III (ATIII Geneva) with defective heparin cofactor activity was characterized by DNA single strand amplification and subsequent direct sequencing. ATIII Geneva was found to have a G to A transition in Exon IIIa leading to an Arg-129 to Gln mutation. This amino acid is part of the ATIII region comprising residues 114-154, which contains the highest proportion of basic residues (Arg or Lys), and is known from chemical modification studies to be involved in heparin binding. The variant protein did not bind heparin-Sepharose and was isolated from the propositus plasma by immunoaffinity chromatography. High affinity (for ATIII) heparin had only a minimal effect on thrombin and activated factor X inhibition by the purified abnormal ATIII. Taken together, these results demonstrate an important role for Arg-129 in the binding and interaction of ATIII with heparin of high affinity. We propose that a cooperation between Lys-125, Arg-129, Lys-136, and Arg-47 exposed at the surface of the inhibitor allows the binding of the essential pentasaccharide domain of heparin which is specific for the ATIII interaction.  相似文献   

14.
15.
Many actin-binding proteins have been shown to possess multiple activities to regulate filament dynamics. Tropomodulins (Tmod1–4) are a conserved family of actin filament pointed end-capping proteins. Our previous work has demonstrated that Tmod3 binds to monomeric actin in addition to capping pointed ends. Here, we show a novel actin-nucleating activity in mammalian Tmods. Comparison of Tmod isoforms revealed that Tmod1–3 but not Tmod4 nucleate actin filament assembly. All Tmods bind to monomeric actin, and Tmod3 forms a 1:1 complex with actin. By truncation and mutagenesis studies, we demonstrated that the second α-helix in the N-terminal domain of Tmod3 is essential for actin monomer binding. Chemical cross-linking and LC-MS/MS further indicated that residues in this second α-helix interact with actin subdomain 2, whereas Tmod3 N-terminal domain peptides distal to this α-helix interact with actin subdomain 1. Mutagenesis of Leu-73 to Asp, which disrupts the second α-helix of Tmod3, decreases both its actin monomer-binding and -nucleating activities. On the other hand, point mutations of residues in the C-terminal leucine-rich repeat domain of Tmod3 (Lys-317 in the fifth leucine-rich repeat β-sheet and Lys-344 or Arg-345/Arg-346 in the C-terminal α6-helix) significantly reduced pointed end-capping and nucleation without altering actin monomer binding. Taken together, our data indicate that Tmod3 binds actin monomers over an extended interface and that nucleating activity depends on actin monomer binding and pointed end-capping activities, contributed by N- and C-terminal domains of Tmod3, respectively. Tmod3 nucleation of actin assembly may regulate the cytoskeleton in dynamic cellular contexts.  相似文献   

16.
17.
Several structural features of the cytoplasmic domain of CD4 including phosphorylation of Ser-408 have been shown to be important in its endocytosis (Shin, J., Doyle, C., Yang, Z., Kappes, D., and Strominger, J.L. (1990) EMBO J. 9, 425-434). A series of cytoplasmic domain truncations have now indicated that the membrane proximal region of the cytoplasmic domain from Arg-396 to Lys-417 is sufficient for phorbol ester-induced internalization; this segment is predicted to be an alpha-helix. The severe impairment of endocytosis resulting from the mutation Ser-408 to Ala-408 is largely restored by a compensating mutation Ala-404 to Ser-404; phosphorylation of Ser-404 has been directly demonstrated. Furthermore, mutation of Met-407, Ile-410, Leu-413, or Leu-414 to a hydrophilic residue eliminated CD4 endocytosis as did domain truncation at Arg-412. Ser-408 was normally phosphorylated in all of these mutants, suggesting that other residues in this region, including the four hydrophobic amino acids, are also required for CD4 endocytosis. Immunofluorescence microscopy following staining of intact and permeabilized cells showed that all endocytosis defective mutants indeed remained on the cell surface even after phorbol ester treatment, while wild type CD4 was endocytosed and degraded in lysosomes. These data indicate that endocytosis requiring residues 397-417 and binding of lymphocyte tyrosine kinase at residues 417-429 are functions of independent segments of the cytoplasmic region and lead to a hypothesis regarding some features of the endocytic process.  相似文献   

18.
The sequential binding of heat shock protein 90 (hsp90) to a series of tetratricopeptide repeat (TPR) proteins is critical to its function as a molecular chaperone. We have used site-directed mutagenesis to clarify the structural basis for the binding of hsp90 to the TPR domain of phosphoprotein phosphatase 5 (PP5). This TPR domain was chosen for study because its three-dimensional structure is known. We examined co-immunoprecipitation of hsp90 with wild type and mutant TPR constructs from transfected cells. Only mutations located on one face of the TPR domain affected hsp90 binding. This allowed the identification of a binding groove. Three basic residues that are highly conserved in hsp90-binding TPR proteins extend prominently into this groove. Lys-97 and Arg-101 were absolutely required for hsp90 binding, while mutation of Arg-74 diminished, but did not abrogate, hsp90 binding. Mutation of Lys-32, another conserved basic residue in the binding groove, also blocked hsp90 binding. The TPR domain of PP5 bound specifically to a 12-kDa C-terminal fragment of hsp90. This binding was reduced by mutation of acidic residues in the hsp90 fragment. These data suggest conservation, among hsp90-binding TPR proteins, of a binding groove containing basic residues that interact with acidic residues near the C terminus of hsp90.  相似文献   

19.
The cyclic AMP-dependent kinase-anchoring proteins (AKAPs) function as scaffolds for a wide-range of protein-protein interactions. The 250-kDa AKAP known as gravin plays a central role in organizing G-protein-coupled receptors to the protein kinases and phosphatases that regulate receptor function in desensitization, resensitization, and sequestration. Although gravin is critical for G-protein-linked receptor biology, the molecular features of the receptor necessary for interaction with this scaffold are not known. Herein, we map the regions of the beta(2)-adrenergic receptor that are required for binding to gravin. Intracellular loops 1, 2, and 3 appear not to participate in the binding of the receptor to the scaffold. In contrast, the C-terminal cytoplasmic region of the receptor (Arg-329 to Leu-413) competes readily for the binding of the beta(2)-adrenergic receptor by gravin, both using in vitro and in vivo assays. C-terminally truncated peptides with sequences ranging from Arg-329 to Leu-342 (13 aminoacyl residues), to Asn-352 (23 residues), to Tyr-366 (37 residues), to Asp-380 (51 residues), or to His-390 (61 residues), as well as N-terminally truncated peptides from Gln-391 to Leu-413 (23 residues) or Leu-381 to Leu-413 (33 residues) displayed no ability to block binding of receptor to gravin. The combination of Arg-329 to His-390 peptide and Gln-391 to Leu-413 peptide, however, reconstitutes a fragmented but full-length C-terminal region and also potently blocks the ability of gravin to bind the beta(2)-adrenergic receptor. The gravin-receptor interaction was examined in response to agonist by confocal microscopy. Remarkably, the association of the receptor with gravin was not disrupted during agonist-induced sequestration. The receptor-scaffold complex was maintained during agonist-induced sequestration. These data, in agreement with the biochemical data, reveal that gravin binds the receptor through the beta(2)-adrenergic receptor C-terminal cytoplasmic domain and that this interaction is maintained as the receptor is internalized. This is the first report of an AKAP scaffold protein translocating with its receptor, in this case a G-protein-coupled receptor.  相似文献   

20.
A segment of inositol 1,4,5-trisphosphate 3-kinase responsible for inositol 1,4,5-trisphosphate (InsP(3)) binding was characterized and confirmed by three different approaches employing the fully active expressed catalytic domain of the enzyme. Part of this moiety was protected from limited tryptic proteolysis by InsP(3). Sequencing of two fragments of 16 and 21 kDa, generated in the absence or presence of InsP(3), respectively, identified segment Glu-271 to Arg-305 as being protected. 15 monoclonal antibodies, all binding to epitopes within this region, inhibited enzyme activity and interfered with inositol phosphate binding. Detailed enzyme kinetic parameters of 32 site-directed mutants revealed residues Arg-276 and Lys-303 in this segment and Arg-322, located nearby, as directly involved in and five other closely neighbored residues, all located within a segment of 73 amino acids, as also influencing InsP(3) binding. Part of this region is similar in sequence to an InsP(3) binding segment in InsP(3) receptors. Combined with the finding that mutants influencing only ATP binding all lie outside this region, these data indicate that an InsP(3) binding core domain is inserted between two segments acting together in ATP binding and phosphate transfer.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号