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.
The fine specificity of the response of T cell clones derived from B10.BR and B10.S congenic mouse strains restricted by I-Ak and I-As molecules, respectively, and which recognize the same 17 amino acid sequence (102-118) of myoglobin, has been investigated and compared with that of T cell clones specific for the same peptide with I-A.d The critical amino acid residues within the 102-118 region of myoglobin required for stimulation of I-Ak-and I-As-restricted T cell clones specific for this determinant were compared using a panel of synthetic peptide analogs. Residues 109, 113, and 116 were critical for stimulation of clones from both haplotypes, although the precise fine specificity varied, even among clones using the same restriction molecule. Residues 109 and 116 are also critical for stimulation of myoglobin-specific I-Ad-restricted clones (Berkower, I., L. A. Matis, G.K. Buckenmeyer, F.R. N. Gurd, D. L. Longo, and J. A. Berzofsky. J. Immunol. 132:1370, 1984). There was also considerable overlap in the size of the minimal determinant necessary for full activity: 106-118 for B10.BR and B10.D2 (Cease, K. B., I. Berkower, J. York-Jolley, and J. A. Berzofsky. J. Exp. Med. 164:1779, 1986) clones and 102-117 for B10.S clones. Despite this similarity in fine specificity, T cell clones were genetically restricted and could not be stimulated with the 102-118 peptide presented by Ia molecules of other haplotypes that could also present this epitope to syngeneic clones. These results suggest that binding of an immunogenic peptide to class II molecules is not sufficient to ensure recognition by a given T cell antigen receptor specific for the peptide, but do not indicate whether the major histocompatibility complex molecules interact directly with the T cell antigen receptor or induce a different recognizable conformation of the peptide.  相似文献   

2.
A cloned, antigen-specific T suppressor cell line derived from a CBA mouse expresses large amounts of I-A and I-E antigens. Comparative two-dimensional polyacrylamid gel electrophoresis of biosynthetically labeled I-A antigens immunoprecipitated with a variety of monoclonal I-Ak-specific antibodies suggested that alpha, beta and Ii polypeptide chains are identical with B-cell-derived I-A. Dimeric complexes formed by I-A chains derived from B or T suppressor cells were also similar with two major exceptions. Pulse-labeled T-cell-derived Ia antigen was complexed with two additional unknown components of about 31K. These components were not visible in pulse-chased (processed) materials. In addition, T suppressor-cell-derived I-A antigens did not contain S-S linked dimers consisting of processed alpha and beta chains, which are usually formed during solubilization of B cells. We consider the possibility that in T cells these chains are associated with other structures, thus preventing S-S linkage between alpha and beta chains.  相似文献   

3.
The residues in an influenza nucleoprotein (NP) cytotoxic T cell determinant necessary for cytotoxic T cell (CTL) recognition, were identified by assaying the ability of hybrid peptides to sensitize a target cell to lysis. The hybrid peptides were formed by substituting amino acids from one determinant (influenza NP 147-158) for the corresponding residues of a second peptide (HLA CW3 171-182) capable of binding to a common class I protein (H-2Kd). Six amino acids resulted in partial recognition; however, the presence of a seventh improved the potency of the peptide. Five of the six amino acids were shown to be required for recognition. The spacing of the six amino acids was consistent with the peptide adopting a helical conformation when bound. The importance of each amino acid in CTL recognition and binding to the restriction element was investigated further by assaying the ability of peptides containing point substitutions either to sensitize target cells or to compete with the natural NP sequence for recognition by CTL. The T cell response was much more sensitive to substitution than the ability of the peptide to bind the restriction element. Collectively the separate strategies identified an approximate conformation and orientation of the peptide when part of the complex and permitted a potential location in the MHC binding site to be identified. The model provides a rationalization for analogues which have previously been shown to exhibit greater affinity for the class I molecule and suggests that the binding site in major histocompatibility complex (MHC) class I molecules might have greater steric constraints that the corresponding area of class II proteins.  相似文献   

4.
The T cell response to lambda-repressor is directed to a 15 amino acid peptide (P12-26) of the protein in A/J mice. Previous studies have demonstrated a preferential use of V alpha 2 and V beta 1 amongst the T cell hybridomas specific for P12-26 in the context of I-Ek. By using the polymerase chain reaction, the sequences of a panel of the T cells using V alpha 2 and V beta 1 were determined. A highly conserved alpha-chain V-J junctional sequence was found in six of the eight T cell hybrids. This consensus alpha-chain VJ sequence may be combined with different members of V alpha 2, indicating a more restricted selection on the junctional region than on the V element in these T cells. In contrast, greater diversities were found on the V-D-J region of beta-chains despite the same V beta 1 and J beta 2.1 were used. However, a highly conserved glutamic acid residue was found at the same position of beta-chains where a similar conservation was identified in cytochrome c-specific T cells. The correlation of the TCR sequence with the fine specificities of these T cells suggests that a single amino acid deletion in the V alpha-J alpha region may reduce the P12-26 response and abolish the recognition of an altered peptide [Phe22] P12-26. In addition, three amino acid difference in the V-D-J region of the beta-chain also determine the P12-26 reactivity. Thus the V(D)J junctional regions of both alpha- and beta-chains may be critical for the recognition of the peptide Ag presented by the specific MHC molecule.  相似文献   

5.
The effect of polymorphic residues on the A alpha A beta molecule on T cell recognition of the N-terminal nonapeptide of myelin basic protein (R1-9) was determined. Ak-restricted T cell clones recognizing R1-9 were isolated. The peptide-Ia specificities of these clones were determined by testing the response to 1) a panel of peptide analogs of R1-11, 2) splenic APC from mice expressing MHC molecules from serologically distinct haplotypes, and 3) L cell transfectants expressing mutant/recombinant A beta cDNA containing combinations of polymorphic nucleotide sequences from the k and u alleles. Comparisons were made between the Ak-restricted clones and a previously characterized panel of Au-restricted clones. Certain Ak-restricted clones were able to recognize MBP peptide analogs that were not recognized by any of the Au-restricted clones. The Au-restricted T cell clones did not cross-react with R1-9 presented in the context of Ak, whereas the majority of the Ak-restricted clones responded to R1-9 presented in the context of Au. This nonreciprocal cross-reactivity was also reflected in the relative responses of the two sets of T cell clones to the interchange of u- and k-derived residues in the A beta chain. Residues in regions corresponding both the alpha-helical or beta-sheet portions of the hypothetical Ia three-dimensional structure were involved. The results suggest that overall specificity of the T cell clones is the summation of numerous distinct subspecificities for different regions of the peptide-Ia ligand. These results indicate that there can be striking differences in T cell specificity for an autoantigenic epitope, even in the context of A alpha A beta molecules from very closely related haplotypes.  相似文献   

6.
A new DR beta-chain allele is defined that is identical to the previously described DR6b molecule except for the first hyperpolymorphic region, where the new allele displays the same polymorphisms found on DR8 and DR12 genes. Two distinct epitopes have been mapped on this new allele. The polymorphism in common with DRw8 and DRw12 is recognized by mAb GS313-9D11. However, alloreactive T cell clones specific for DR6b cells (Dw9) recognize this allele, whereas Dw8-specific T cell clones do not. The mAb determinant maps to the first beta-sheet and probably involves a polymorphic residue lying outside the helix. The binding of mAb 9D11 to this region does not interfere with TCR binding. Alloreactive T cell recognition is associated with polymorphisms located predominantly on the alpha-helical portion of the molecule.  相似文献   

7.
8.
MHC proteins are polymorphic cell surface glycoproteins involved in the binding of peptide Ag and their presentation to T lymphocytes. The polymorphic amino acids of MHC proteins are primarily located in the N-terminal domains and are thought to influence T cell recognition both by influencing the binding of peptide Ag and by direct contact with the T cell receptor. In order to determine the relative importance of individual polymorphic amino acids in Ag presentation, a number of groups have taken the approach of interchanging polymorphic amino acids between different alleles of MHC protein in an attempt to define which of the polymorphisms influence peptide binding and which influence T cell recognition by direct contact with the TCR. The peptide OVA323-339 has been previously shown to bind to the MHC class II protein Ad and to have a much lower affinity for Ak, whereas the peptide hen egg lysozyme 46-61 binds well to Ak and poorly to Ad. In the present report, we have analyzed the ability of purified wild-type MHC class II proteins as well as the ability of three different hybrid molecules between Ad and Ak to bind and present these peptides. We find that the alpha-chain of the MHC class II protein plays a critical role in the binding of HEL46-61 and confers the specificity for binding OVA323-339, regardless of which beta-chain is present. We also find that the beta-chain region 65-67 does not control the specificity of peptide binding to the MHC protein, but is important in T cell responses to preformed MHC-peptide complexes, suggesting a role for this region in contacting the TCR.  相似文献   

9.
Chien CH  Tsai CH  Lin CH  Chou CY  Chen X 《Biochemistry》2006,45(23):7006-7012
The prolyl dipeptidase DPP-IV plays diverse and important roles in cellular functions. It is a membrane-bound exoprotease involved in the proteolytic cleavage of several insulin-sensing hormones. The inhibition of its enzymatic activity has been proven effective in the treatment of type II diabetes. Homodimeric DPP-IV interacts extracellularly with adenosine deaminase, and this interaction is critical for adenosine signaling and T-cell proliferation. In this study, we investigated the contribution of hydrophobic interactions to the dimerization of DPP-IV. Hydrophobic residues F713, W734, and Y735 were found to be essential for DPP-IV dimerization. Moreover, the enzymatic activity of DPP-IV was correlated with its quaternary structure. Monomeric DPP-IV had only residual activity left, ranging from 1/30 to 1/1600 of the dimeric forms. Using a surface plasmon resonance technique, we demonstrated that the affinity of these DPP-IV monomers for adenosine deaminase was not significantly altered, compared to that of dimeric DPP-IV. The study not only identifies the hydrophobic interactions critical for DPP-IV dimer formation, but also reveals no global conformational change upon the formation of monomers as determined by the protein-protein interaction (Kd) of DPP-IV with adenosine deaminase.  相似文献   

10.
Jackman JE  Phizicky EM 《Biochemistry》2008,47(16):4817-4825
The yeast tRNA(His) guanylyltransferase (Thg1) is an essential enzyme in yeast. Thg1 adds a single G residue to the 5' end of tRNA(His) (G(-1)), which serves as a crucial determinant for aminoacylation of tRNA(His). Thg1 is the only known gene product that catalyzes the 3'-5' addition of a single nucleotide via a normal phosphodiester bond, and since there is no identifiable sequence similarity between Thg1 and any other known enzyme family, the mechanism by which Thg1 catalyzes this unique reaction remains unclear. We have altered 29 highly conserved Thg1 residues to alanine, and using three assays to assess Thg1 catalytic activity and substrate specificity, we have demonstrated that the vast majority of these highly conserved residues (24/29) affect Thg1 function in some measurable way. We have identified 12 Thg1 residues that are critical for G(-1) addition, based on significantly decreased ability to add G(-1) to tRNA(His) in vitro and significant defects in complementation of a thg1Delta yeast strain. We have also identified a single Thg1 alteration (D68A) that causes a dramatic decrease in the rigorous specificity of Thg1 for tRNA(His). This single alteration enhances the k(cat)/K(M) for ppp-tRNA(Phe) by nearly 100-fold relative to that of wild-type Thg1. These results suggest that Thg1 substrate recognition is at least in part mediated by preventing recognition of incorrect substrates for nucleotide addition.  相似文献   

11.
Tai N  Ding Y  Schmitz JC  Chu E 《Nucleic acids research》2002,30(20):4481-4488
Previous studies have shown that human dihydrofolate reductase (DHFR) acts as an RNA-binding protein, in which it binds to its own mRNA and, in so doing, results in translational repression. In this study, we used RNA gel mobility shift and nitrocellulose filter-binding assays to further investigate the specificity of the interaction between human DHFR protein and human DHFR mRNA. Site-directed mutagenesis was used to identify the critical amino acid residues on DHFR protein required for RNA recognition. Human His-Tag DHFR protein specifically binds to human DHFR mRNA, while unrelated proteins including thymidylate synthase, p53 and glutathione-S-transferase were unable to form a ribonucleoprotein complex with DHFR mRNA. The Cys6 residue is essential for RNA recognition, as mutation at this amino acid with either an alanine (C6A) or serine (C6S) residue almost completely abrogated RNA-binding activity. Neither one of the cysteine mutant proteins was able to repress the in vitro translation of human DHFR mRNA. Mutations at amino acids Ile7, Arg28 and Phe34, significantly reduced RNA-binding activity. An RNA footprinting analysis identified three different RNA sequences, bound to DHFR protein, ranging in size from 16 to 45 nt, while a UV cross-linking analysis isolated an ~16 nt RNA sequence bound to DHFR. These studies begin to identify the critical amino acid residues on human DHFR that mediate RNA binding either through forming direct contact points with RNA or through maintaining the protein in an optimal structure that allows for the critical RNA-binding domain to be accessible.  相似文献   

12.
The initiation and elongation stages of translation are directed by codon-anticodon interactions. In contrast, a release factor protein mediates stop codon recognition prior to polypeptide chain release. Previous studies have identified specific regions of eukaryotic release factor one (eRF1) that are important for decoding each stop codon. The cavity model for eukaryotic stop codon recognition suggests that three binding pockets/cavities located on the surface of eRF1's domain one are key elements in stop codon recognition. Thus, the model predicts that amino acid changes in or near these cavities should influence termination in a stop codon-dependent manner. Previous studies have suggested that the TASNIKS and YCF motifs within eRF1 domain one play important roles in stop codon recognition. These motifs are highly conserved in standard code organisms that use UAA, UAG, and UGA as stop codons, but are more divergent in variant code organisms that have reassigned a subset of stop codons to sense codons. In the current study, we separately introduced TASNIKS and YCF motifs from six variant code organisms into eRF1 of Saccharomyces cerevisiae to determine their effect on stop codon recognition in vivo. We also examined the consequences of additional changes at residues located between the TASNIKS and YCF motifs. Overall, our results indicate that changes near cavities two and three frequently mediated significant effects on stop codon selectivity. In particular, changes in the YCF motif, rather than the TASNIKS motif, correlated most consistently with variant code stop codon selectivity.  相似文献   

13.
YopH is a 468-amino acid protein-tyrosine phosphatase that is produced by pathogenic Yersinia species. YopH is translocated into host mammalian cells via a type III protein secretion system. Translocation of YopH into human epithelial cells results in dephosphorylation of p130(Cas) and paxillin, disruption of focal adhesions, and inhibition of integrin-mediated bacterial phagocytosis. Previous studies have shown that the N-terminal 129 amino acids of YopH comprise a bifunctional domain. This domain binds to the SycH chaperone in Yersinia to orchestrate translocation and to tyrosine-phosphorylated target proteins in host cells to mediate substrate recognition. We used random mutagenesis in combination with the yeast two-hybrid system to identify residues in the YopH N-terminal domain that are involved in substrate-binding activity. Four single codon changes (Q11R, V31G, A33D, and N34D) were identified that interfered with binding of the YopH N-terminal domain to tyrosine-phosphorylated p130(Cas) but not to SycH. These mutations did not impair YopH translocation into HeLa cells infected with Yersinia pseudotuberculosis. Introduction of the V31G substitution into catalytically inactive (substrate-trapping) forms of YopH interfered with the ability of these proteins to bind to p130(Cas) and to localize to focal adhesions in HeLa cells. In addition, the V31G substitution reduced the ability of catalytically active YopH to dephosphorylate target proteins in HeLa cells. These data indicate that the substrate- and SycH-binding activities of the YopH N-terminal domain can be separated and that the former activity is important for recognition and dephosphorylation of substrates by YopH in vivo.  相似文献   

14.
The linker for activation of T cells (LAT) is essential for signaling through the T cell receptor (TCR). Following TCR stimulation, LAT becomes tyrosine-phosphorylated, creating docking sites for other signaling proteins such as phospholipase C-gamma(1) (PLC-gamma(1)), Grb2, and Gads. In this study, we have attempted to identify the critical tyrosine residues in LAT that mediate TCR activation-induced mobilization of intracellular Ca(2+) and activation of the MAP kinase Erk2. By using the LAT-deficient Jurkat derivative, J.CaM2, stable cell lines were established expressing various tyrosine mutants of LAT. We show that three specific tyrosine residues (Tyr(132), Tyr(171), and Tyr(191)) are necessary and sufficient to achieve a Ca(2+) flux following TCR stimulation. These tyrosine residues function by reconstituting PLC-gamma(1) phosphorylation and recruitment to LAT. However, these same tyrosines can only partially reconstitute Erk activation. Full reconstitution of Erk requires two additional tyrosine residues (Tyr(110) and Tyr(226)), both of which have the Grb2-binding motif YXN. This reconstitution of Erk activation requires that the critical tyrosine residues be on the same molecule of LAT, suggesting that a single LAT molecule nucleates multiple protein-protein interactions required for optimal signal transduction.  相似文献   

15.
Interleukin 2-dependent alloreactive cytotoxic T cell lines, with activity predominantly directed against the HLA-A2 antigen, have been generated in vitro by stimulating blood mononuclear cells from donors nonimmune to the Epstein-Barr (EB) virus with appropriate numbers of EB virus-transformed B cells from A2-homozygous individuals. Such effector cells were tested against a panel of EB virus-transformed target cell lines all expressing the serologically defined A2 antigen but typed into common A2 and variant A2 subgroups on the basis of their recognition by A2-restricted EB virus-specific cytotoxic T cells. Variant A2 responder cells cocultivated with common A2-bearing stimulators gave rise to effector T cell lines which recognized only the common A2-bearing subgroup of targets. By contrast, responder cells from A2-negative donors stimulated with common A2-bearing cells produced effector T cell lines in which the strong lysis of common A2-bearing targets was accompanied by a lower, but still significant, lysis directed against all targets within the variant A2 subgroup. In both cases, lysis of the target cells was blocked equally well by the anti-A2-specific monoclonal antibody MA2.1 as by the monoclonal antibody W6/32 specific for HLA-A, -B, and -C determinants. This suggests that HLA-A2 molecules possess at least two distinct sets of epitopes capable of inducing alloreactive T cell cytotoxicity: first, epitopes probably associated with T cell-restricting sites, which generate subgroup-specific responses, and second, epitopes shared by all A2 molecules, and perhaps associated with serologically defined sites, which generate pan A2 group-specific responses.Abbreviations used in this paper EB Epstein-Barr - IL-2 Interleukin 2 - UM unfractionated mononuclear - AET aminoethylisothiouroniumbromide hydrobromide  相似文献   

16.
Granulomatous inflammation in schistosomiasis is strictly dependent on CD4+ Th lymphocytes sensitized to egg Ags, but its intensity is genetically regulated. C3H and CBA (H-2k) are strains of mice that develop large granulomas; they also strongly respond to the major egg Ag Sm-p40. We now show that the immunodominant epitope recognized by CD4+ Th cells from infected H-2k mice is confined to 13-mer peptide 234-246 (PKSDNQIKAVPAS), which elicits an I-Ak-restricted Th1-type response. Using a panel of alanine-monosubstituted peptides, we identified Asp237 as the main contact residue with I-Ak. On the other hand, three TCR contact residues were essential to stimulate epitope-specific T cell hybridomas: for two hybridomas these were Asn238, Gln239, and Lys241; and for one, Asn238, Lys241, and Pro244. In one instance, alanine substitution for Gln239 generated an antagonist that blocked subsequent stimulation with wild-type peptide. Most importantly, replacement of Asn238, Gln239, or Lys241 caused a profound loss of polyclonal CD4+ T cell reactivity from schistosome-infected mice. This study identifies the critical residues of immunodominant peptide 234-246 involved in the T cell response against the Sm-p40 egg Ag and suggests that suitable altered peptides may be capable of precipitating its down-regulation.  相似文献   

17.
T cell receptor recognition of peptide/MHC has been described as proceeding through a "two-step" process in which the TCR first contacts the MHC molecule prior to formation of the binding transition state using the germline-encoded CDR1 and CDR2 loops. The receptor then contacts the peptide using the hypervariable CDR3 loops as the transition state decays to the bound state. The model subdivides TCR binding into peptide-independent and peptide-dependent steps, demarcated at the binding transition state. Investigating the two-step model, here we show that two TCRs that recognize the same peptide/MHC bury very similar amounts of solvent-accessible surface area in their transition states. However, 1300-1500 A2 of surface area is buried in each, a significant amount suggestive of participation of peptide and associated CDR3 surface. Consistent with this interpretation, analysis of peptide and TCR variants indicates that stabilizing contacts to the peptide are formed within both transition states. These data are incompatible with the original two-step model, as are transition state models built using the principle of minimal frustration commonly employed in the investigation of protein folding and binding transition states. These findings will be useful in further explorations of the nature of TCR binding transition states, as well as ongoing efforts to understand the mechanisms by which T cell receptors recognize the composite peptide/MHC surface.  相似文献   

18.
T cell receptor beta-chain selection in human allograft rejection   总被引:8,自引:0,他引:8  
We have analyzed a series of T cell lines established from renal needle biopsies taken from renal allograft recipients with clinical signs of rejection. These T cells show strong cytotoxicity directed against donor HLA and their proliferative capacity in vitro is highly correlated with irreversible graft rejection. A total of 10 of 12 lines examined by Southern blot analysis using a J beta C beta DNA probe show predominant beta-chain rearrangements. In one instance DNA was isolated from cell lines generated from sequential biopsies taken from the same patient at different times of rejection. These lines show the same predominant beta-chain rearrangements. To determine whether these predominant rearrangements are due to expansion of a single clone or different T cell clones rearranging similar beta-chains, the same blots were analyzed with a J gamma probe. Cell line MH3 shows two predominant beta-chain rearrangements and at least seven of eight possible rearranged gamma-chain bands, implying that multiple clones share similar beta-chains. In contrast, the cell line King shows a single beta-chain and a single gamma-chain rearrangement. Many of the other cell lines fall between these two extremes, indicating that both beta-chain selection and clonal dominance are operating during graft rejection, resulting in the appearance of predominant beta-chain rearrangements.  相似文献   

19.
Replication of human cytomegalovirus is controlled by a vigorous CD8 T cell response. The persistent nature of infection is believed to periodically stimulate T cell responses resulting in considerable expansions of virus-specific CD8 T cells over time. In this study, we describe the magnitude and breadth of CD8 T cell responses against the immunodominant viral Ags, IE-1 and pp65, in acute and long-term infection using the IFN-gamma ELISPOT assay. Simultaneously, we have identified several novel MHC class I restricted CD8 T cell epitopes. Acute phase responses in immunocompetent donors appear to be extremely focused as early as 1 week post diagnosis with dominant peptide-specific responses observed against both proteins. These dominant responses remain detectable at all later time points over a 4-year follow-up. Interestingly the IE-1 responses show an increase over time whereas the pp65 responses do not, which contrasts with data showing that responses against both Ags are elevated in elderly individuals. We also observe the rapid emergence of an effector memory phenotype for virus-specific CD8 T cells as observed in persistent infection. Over time the revertant CD45RA(pos) effector cell population is also expanded, and this is more evident in the preferentially expanded IE-1 responses. We postulate that periodic low-level virus reactivation after the acute infection phase preferentially stimulates these responses whereas pp65-specific T cell expansions probably occur during the infrequent episodes of lytic viral replication or secondary infection.  相似文献   

20.
Plasmatocyte spreading peptide (PSP) is a 23-amino acid cytokine that induces a class of insect immune cells called plasmatocytes to spread on foreign surfaces. The structure of PSP consists of a disordered N terminus (residues 1-6) and a well-defined core (residues 7-23) stabilized by a disulfide bridge between Cys(7) and Cys(19), hydrophobic interactions, and a short beta-hairpin. Structural comparisons also indicate that the core region of PSP adopts an epidermal growth factor (EGF)-like fold very similar to the C-terminal subdomain of EGF-like module 5 of thrombomodulin. To identify residues important for plasmatocyte spreading activity, we bioassayed PSP mutants in which amino acids were either replaced with alanine or deleted. Within the well-defined core of PSP, alanine replacement of Cys(7) and Cys(19) (C7.19A) eliminated all activity. Alanine replacement of Arg(13) reduced activity approximately 1000-fold in comparison to wild-type PSP, whereas replacement of the other charged residues (Asp(16), Arg(18), Lys(20)) surrounding Cys(19) diminished activity to a lesser degree. The point mutants Y11A, T14A, T22A, and F23A had activity identical or only slightly reduced to that of wild-type PSP. The mutant PSP-(7-23) lacked the entire unstructured domain of PSP and was found to have no plasmatocyte spreading activity. Surprisingly, E1A and N2A had higher activity than wild-type PSP, but F3A had almost no activity. We thus concluded that the lack of activity for PSP-(7-23) was largely due to the critical importance of Phe(3). To determine whether reductions in activity correlated with alterations in tertiary structure, we compared the C7.19A, R13A, R18A, and F3A mutants to wild-type PSP by NMR spectroscopy. As expected, the simultaneous replacement of Cys(7) and Cys(19) profoundly affected tertiary structure, but the R13A, R18A, and F3A mutants did not differ from wild-type PSP. Collectively, these results indicate that residues in both the unstructured and structured domains of PSP are required for plasmatocyte-spreading activity.  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