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1.
    
The genome of the diurnal cyanobacterium Cyanothece sp. PCC 51142 has recently been sequenced and observed to contain 35 pentapeptide repeat proteins (PRPs). These proteins, while present throughout the prokaryotic and eukaryotic kingdoms, are most abundant in cyanobacteria. The sheer number of PRPs in cyanobacteria coupled with their predicted location in every cellular compartment argues for important, yet unknown, physiological and biochemical functions. To gain biochemical insights, the crystal structure for Rfr32, a 167-residue PRP with an N-terminal 29-residue signal peptide, was determined at 2.1 A resolution. The structure is dominated by 21 tandem pentapeptide repeats that fold into a right-handed quadrilateral beta-helix, or Rfr-fold, as observed for the tandem pentapeptide repeats in the only other PRP structure, the mycobacterial fluoroquinoline resistance protein MfpA from Mycobacterium tuberculosis. Sitting on top of the Rfr-fold are two short, antiparallel alpha-helices, bridged with a disulfide bond, that perhaps prevent edge-to-edge aggregation at the C terminus. Analysis of the main-chain (Phi,Psi) dihedral orientations for the pentapeptide repeats in Rfr32 and MfpA makes it possible to recognize the structural details for the two distinct types of four-residue turns adopted by the pentapeptide repeats in the Rfr-fold. These turns, labeled type II and type IV beta-turns, may be universal motifs that shape the Rfr-fold in all PRPs.  相似文献   

2.
    
The processive beta-strands and turns of a polypeptide parallel beta-helix represent one of the topologically simplest beta-sheet folds. The three subunits of the tailspike adhesin of phage P22 each contain 13 rungs of a parallel beta-helix followed by an interdigitated section of triple-stranded beta-helix. Long stacks of hydrophobic residues dominate the elongated buried core of these two beta-helix domains and extend into the core of the contiguous triple beta-prism domain. To test whether these side-chain stacks represent essential residues for driving the chain into the correct fold, each of three stacked phenylalanine residues within the buried core were substituted with less bulky amino acids. The mutant chains with alanine in place of phenylalanine were defective in intracellular folding. The chains accumulated exclusively in the aggregated inclusion body state regardless of temperature of folding. These severe folding defects indicate that the stacked phenylalanine residues are essential for correct parallel beta-helix folding. Replacement of the same phenylalanine residues with valine or leucine also impaired folding in vivo, but with less severity. Mutants were also constructed in a second buried stack that extends into the intertwined triple-stranded beta-helix and contiguous beta-prism regions of the protein. These mutants exhibited severe defects in later stages of chain folding or assembly, accumulating as misfolded but soluble multimeric species. The results indicate that the formation of the buried hydrophobic stacks is critical for the correct folding of the parallel beta-helix, triple-stranded beta-helix, and beta-prism domains in the tailspike protein.  相似文献   

3.
    
Several proteins and peptides that can convert from alpha-helical to beta-sheet conformation and form amyloid fibrils, including the amyloid beta-peptide (Abeta) and the prion protein, contain a discordant alpha-helix that is composed of residues that strongly favor beta-strand formation. In their native states, 37 of 38 discordant helices are now found to interact with other protein segments or with lipid membranes, but Abeta apparently lacks such interactions. The helical propensity of the Abeta discordant region (K16LVFFAED23) is increased by introducing V18A/F19A/F20A replacements, and this is associated with reduced fibril formation. Addition of the tripeptide KAD or phospho-L-serine likewise increases the alpha-helical content of Abeta(12-28) and reduces aggregation and fibril formation of Abeta(1-40), Abeta(12-28), Abeta(12-24), and Abeta(14-23). In contrast, tripeptides with all-neutral, all-acidic or all-basic side chains, as well as phosphoethanolamine, phosphocholine, and phosphoglycerol have no significant effects on Abeta secondary structure or fibril formation. These data suggest that in free Abeta, the discordant alpha-helix lacks stabilizing interactions (likely as a consequence of proteolytic removal from a membrane-associated precursor protein) and that stabilization of this helix can reduce fibril formation.  相似文献   

4.
  总被引：2，自引：0，他引：2  
Two-dimensional nuclear magnetic resonance spectroscopy was used to investigate the flexibility of the threonine side chains in the beta-helical Tenebrio molitor antifreeze protein (TmAFP) at low temperatures. From measurement of the (3)J(alphabeta) (1)H-(1)H scalar coupling constants, the chi(1) angles and preferred rotamer populations can be calculated. It was determined that the threonines on the ice-binding face of the protein adopt a preferred rotameric conformation at near freezing temperatures, whereas the threonines not on the ice-binding face sample many rotameric states. This suggests that TmAFP maintains a preformed ice-binding conformation in solution, wherein the rigid array of threonines that form the AFP-ice interface matches the ice crystal lattice. A key factor in binding to the ice surface and inhibition of ice crystal growth appears to be the close surface-to-surface complementarity between the AFP and crystalline ice, and the lack of an entropic penalty associated with freezing out motions in a flexible ligand.  相似文献   

5.
In this study, we have analyzed experimentally the helical intrinsic propensities of non-charged and non-aromatic residues at different C-terminal positions (C1, C2, C3) of an Ala-based peptide. The effect was found to be complex, resulting in extra stabilization or destabilization, depending on guest amino acid and position under consideration. Polar (Ser, Thr, Cys, Asn, and Gln) amino acids and Gly were found to have significantly larger helical propensities at several C-terminal positions compared with the alpha-helix center (-1.0 kcal/mole in some cases). Some of the nonpolar residues, especially beta-branched ones (Val and Ile) are significantly more favorable at position C3 (-0.3 to -0.4 kcal/mole), although having minor differences at other C-terminal positions compared with the alpha-helix center. Leu has moderate (-0.1 to -0.2 kcal/mole) stabilization effects at position C2 and C3, whereas being relatively neutral at C1. Finally, Met was found to be unfavorable at C1 and C2 ( +0.2 kcal/mole) and favorable at C3 (-0.2 kcal/mole). Thus, significant differences found between the intrinsic helical propensities at the C-terminal positions and those in the alpha-helix center must be accounted for in helix/coil transition theories and in protein design.  相似文献   

6.
    
To examine how a short secondary structural element derived from a native protein folds when in a different protein environment, we inserted an 11-residue beta-sheet segment (cassette) from human immunoglobulin fold, Fab new, into an alpha-helical coiled-coil host protein (cassette holder). This de novo design protein model, the structural cassette mutagenesis (SCM) model, allows us to study protein folding principles involving both short- and long-range interactions that affect secondary structure stability and conformation. In this study, we address whether the insertion of this beta-sheet cassette into the alpha-helical coiled-coil protein would result in conformational change nucleated by the long-range tertiary stabilization of the coiled-coil, therefore overriding the local propensity of the cassette to form beta-sheet, observed in its native immunoglobulin fold. The results showed that not only did the nucleating helices of the coiled-coil on either end of the cassette fail to nucleate the beta-sheet cassette to fold with an alpha-helical conformation, but also the entire chimeric protein became a random coil. We identified two determinants in this cassette that prevented coiled-coil formation: (1) a tandem dipeptide NN motif at the N-terminal of the beta-sheet cassette, and (2) the hydrophilic Ser residue, which would be buried in the hydrophobic core if the coiled-coil structure were to fold. By amino acid substitution of these helix disruptive residues, that is, either the replacement of the NN motif with high helical propensity Ala residues or the substitution of Ser with Leu to enhance hydrophobicity, we were able to convert the random coil chimeric protein into a fully folded alpha-helical coiled-coil. We hypothesized that this NN motif is a \"secondary structural specificity determinant\" which is very selective for one type of secondary structure and may prevent neighboring residues from adopting an alternate protein fold. These sequences with secondary structural specificity determinants have very strong local propensity to fold into a specific secondary structure and may affect overall protein folding by acting as a folding initiation site.  相似文献   

7.
  总被引：13，自引：1，他引：13  
We report the discovery of a novel family of proteins, each member contains tandem pentapeptide (five residue) repeats, described by the motif A(D/N)LXX. Members of this family are both membrane bound and cytoplasmic. The function of these repeats is uncertain, but they may have a targeting or structural function rather than enzymatic activity. This family is most common in cyanobacteria, suggesting a function related to cyanobacterial-specific metabolism. Although no experimental information is available for the structure of this family, it is predicted that the tandem pentapeptide repeats will form a right-handed beta-helical structure. A structural model of the pentapeptide repeats is presented.  相似文献   

8.
    
We have recently reported on the design of a 20-residue peptide able to form a significant population of a three-stranded up-and-down antiparallel beta-sheet in aqueous solution. To improve our beta-sheet model in terms of the folded population, we have modified the sequences of the two 2-residue turns by introducing the segment DPro-Gly, a sequence shown to lead to more rigid type II' beta-turns. The analysis of several NMR parameters, NOE data, as well as Deltadelta(CalphaH), DeltadeltaC(beta), and Deltadelta(Cbeta) values, demonstrates that the new peptide forms a beta-sheet structure in aqueous solution more stable than the original one, whereas the substitution of the DPro residues by LPro leads to a random coil peptide. This agrees with previous results on beta-hairpin-forming peptides showing the essential role of the turn sequence for beta-hairpin folding. The well-defined beta-sheet motif calculated for the new designed peptide (pair-wise RMSD for backbone atoms is 0.5 +/- 0.1 A) displays a high degree of twist. This twist likely contributes to stability, as a more hydrophobic surface is buried in the twisted beta-sheet than in a flatter one. The twist observed in the up-and-down antiparallel beta-sheet motifs of most proteins is less pronounced than in our designed peptide, except for the WW domains. The additional hydrophobic surface burial provided by beta-sheet twisting relative to a \"flat\" beta-sheet is probably more important for structure stability in peptides and small proteins like the WW domains than in larger proteins for which there exists a significant contribution to stability arising from their extensive hydrophobic cores.  相似文献   

9.
    
Autonomously folding beta-hairpins (two-strand antiparallel beta-sheets) have become increasingly valuable tools for probing the forces that control peptide and protein conformational preferences. We examine the effects of variations in sequence and solvent on the stability of a previously designed 12-residue peptide (1). This peptide adopts a beta-hairpin conformation containing a two-residue loop (D-Pro-Gly) and a four-residue interstrand sidechain cluster that is observed in the natural protein GB1. We show that the conformational propensity of the loop segment plays an important role in beta-hairpin stability by comparing 1 with (D)P--> N mutant 2. In addition, we show that the sidechain cluster contributes both to conformational stability and to folding cooperativity by comparing 1 with mutant 3, in which two of the four cluster residues have been changed to serine. Thermodynamic analysis suggests that the high loop-forming propensity of the (D)PG segment decreases the entropic cost of beta-hairpin formation relative to the more flexible NG segment, but that the conformational rigidity of (D)PG may prevent optimal contacts between the sidechains of the GB1-derived cluster. The enthalpic favorability of folding in these designed beta-hairpins suggests that they are excellent scaffolds for studying the fundamental mechanisms by which amino acid sidechains interact with one another in folded proteins.  相似文献   

10.
    
A model for prediction of alpha-helical regions in amino acid sequences has been tested on the mainly-alpha protein structure class. The modeling represents the construction of a continuous hypothetical alpha-helical conformation for the whole protein chain, and was performed using molecular mechanics tools. The positive prediction of alpha-helical and non-alpha-helical pentapeptide fragments of the proteins is 79%. The model considers only local interactions in the polypeptide chain without the influence of the tertiary structure. It was shown that the local interaction defines the alpha-helical conformation for 85% of the native alpha-helical regions. The relative energy contributions to the energy of the model were analyzed with the finding that the van der Waals component determines the formation of alpha-helices. Hydrogen bonds remain at constant energy independently whether alpha-helix or non-alpha-helix occurs in the native protein, and do not determine the location of helical regions. In contrast to existing methods, this approach additionally permits the prediction of conformations of side chains. The model suggests the correct values for ~60% of all chi-angles of alpha-helical residues.  相似文献   

11.
    
The energy landscape of a peptide [Ace-Lys-Gln-Cys-Arg-Glu-Arg-Ala-Nme] in explicit water was studied with a multicanonical molecular dynamics simulation, and the AMBER parm96 force field was used for the energy calculation. The peptide was taken from the recognition helix of the DNA-binding protein, c-MYB: A rugged energy landscape was obtained, in which the random-coil conformations were dominant at room temperature. The CD spectra of the synthesized peptide revealed that it is in the random state at room temperature. However, the 300 K canonical ensemble, Q(300K), contained alpha-helix, 3(10)-helix, beta-turn, and beta-hairpin structures with small but notable probabilities of existence. The complete alpha-helix, imperfect alpha-helix, and random-coil conformations were separated from one another in the conformational space. This means that the peptide must overcome energy barriers to form the alpha-helix. The overcoming process may correspond to the hydrogen-bond rearrangements from peptide-water to peptide-peptide interactions. The beta-turn, imperfect 3(10)-helix, and beta-hairpin structures, among which there are no energy barriers at 300 K, were embedded in the ensemble of the random-coil conformations. Two types of beta-hairpin with different beta-turn regions were observed in Q(300K). The two beta-hairpin structures may have different mechanisms for the beta-hairpin formation. The current study proposes a scheme that the random state of this peptide consists of both ordered and disordered conformations. In contrast, the energy landscape obtained from the parm94 force field was funnel like, in which the peptide formed the helical conformation at room temperature and random coil at high temperature.  相似文献   

12.
    
The role of hither-to-fore unrecognized long-range hydrogen bonds between main-chain amide hydrogens and polar side chains on the stability of a well-studied (betaalpha)8, TIM barrel protein, the alpha subunit of tryptophan synthase (alphaTS), was probed by mutational analysis. The F19-D46 and I97-D124 hydrogen bonds link the N terminus of a beta-strand with the C terminus of the succeeding antiparallel alpha-helix, and the A103-D130 hydrogen bond links the N terminus of an alpha-helix with the C terminus of the succeeding antiparallel beta-strand, forming clamps for the respective betaalpha or alphabeta hairpins. The individual replacement of these aspartic acid side chains with alanine leads to what appear to be closely related partially folded structures with significantly reduced far-UV CD ellipticity and thermodynamic stability. Comparisons with the effects of eliminating another main-chain-side-chain hydrogen bond, G26-S33, and two electrostatic side-chain-side-chain hydrogen bonds, D38-H92 and D112-H146, all in the same N-terminal folding unit of alphaTS, demonstrated a unique role for the clamp interactions in stabilizing the native barrel conformation. Because neither the asparagine nor glutamic acid variant at position 46 can completely reproduce the spectroscopic, thermodynamic, or kinetic folding properties of aspartic acid, both size and charge are crucial to its unique role in the clamp hydrogen bond. Kinetic studies suggest that the three clamp hydrogen bonds act in concert to stabilize the transition state leading to the fully folded TIM barrel motif.  相似文献   

13.
    
The amino acid composition and architecture of all beta-barrel membrane proteins of known three-dimensional structure have been examined to generate information that will be useful in identifying beta-barrels in genome databases. The database consists of 15 nonredundant structures, including several novel, recent structures. Known structures include monomeric, dimeric, and trimeric beta-barrels with between 8 and 22 membrane-spanning beta-strands each. For this analysis the membrane-interacting surfaces of the beta-barrels were identified with an experimentally derived, whole-residue hydrophobicity scale, and then the barrels were aligned normal to the bilayer and the position of the bilayer midplane was determined for each protein from the hydrophobicity profile. The abundance of each amino acid, relative to the genomic abundance, was calculated for the barrel exterior and interior. The architecture and diversity of known beta-barrels was also examined. For example, the distribution of rise-per-residue values perpendicular to the bilayer plane was found to be 2.7 +/- 0.25 A per residue, or about 10 +/- 1 residues across the membrane. Also, as noted by other authors, nearly every known membrane-spanning beta-barrel strand was found to have a short loop of seven residues or less connecting it to at least one adjacent strand. Using this information we have begun to generate rapid screening algorithms for the identification of beta-barrel membrane proteins in genomic databases. Application of one algorithm to the genomes of Escherichia coli and Pseudomonas aeruginosa confirms its ability to identify beta-barrels, and reveals dozens of unidentified open reading frames that potentially code for beta-barrel outer membrane proteins.  相似文献   

14.
Esterases form a diverse class of enzymes of largely unknown physiological role. Because many drugs and pesticides carry ester functions, the hydrolysis of such compounds forms at least one potential biological function. Carboxylesterases catalyze the hydrolysis of short chain aliphatic and aromatic carboxylic ester compounds. Esterases, D-alanyl-D-alanine-peptidases (DD-peptidases) and beta-lactamases can be grouped into two distinct classes of hydrolases with different folds and topologically unrelated catalytic residues, the one class comprising of esterases, the other one of beta-lactamases and DD-peptidases. The chemical reactivities of esters and beta-lactams towards hydrolysis are quite similar, which raises the question of which factors prevent esterases from displaying beta-lactamase activity and vice versa. Here we describe the crystal structure of EstB, an esterase isolated from Burkholderia gladioli. It shows the protein to belong to a novel class of esterases with homology to Penicillin binding proteins, notably DD-peptidase and class C beta-lactamases. Site-directed mutagenesis and the crystal structure of the complex with diisopropyl-fluorophosphate suggest Ser75 within the "beta-lactamase" Ser-x-x-Lys motif to act as catalytic nucleophile. Despite its structural homology to beta-lactamases, EstB shows no beta-lactamase activity. Although the nature and arrangement of active-site residues is very similar between EstB and homologous beta-lactamases, there are considerable differences in the shape of the active site tunnel. Modeling studies suggest steric factors to account for the enzyme's selectivity for ester hydrolysis versus beta-lactam cleavage.  相似文献   

15.
    
Human acidic fibroblast growth factor (FGF-1) has a beta-trefoil structure, one of the fundamental protein superfolds. The X-ray crystal structures of wild-type and various mutant forms of FGF-1 have been solved in five different space groups: C2, C222(1), P2(1) (four molecules/asu), P2(1) (three molecules/asu), and P2(1)2(1)2(1). These structures reveal two characteristically different conformations for the beta8/beta9 beta-hairpin comprising residue positions 90-94. This region in the wild-type FGF-1 structure (P2(1), four molecules/asu), a his-tagged His93-->Gly mutant (P2(1), three molecules/asu) and a his-tagged Asn106-->Gly mutant (P2(1)2(1)2(1)) adopts a 3:5 beta-hairpin known as a type I (1-4) G1 beta-bulge (containing a type I turn). However, a his-tagged form of wild-type FGF-1 (C222(1)) and a his-tagged Leu44-->Phe mutant (C2) adopt a 3:3 beta-hairpin (containing a type I' turn) for this same region. A feature that distinguishes these two types of beta-hairpin structures is the number and location of side chain positions with eclipsed C(beta) and main-chain carbonyl oxygen groups (Psi is equivalent to +60 degrees). The effects of glycine mutations upon stability, at positions within the hairpin, have been used to identify the most likely structure in solution. Type I' turns in the structural data bank are quite rare, and a survey of these turns reveals that a large percentage exhibit crystal contacts within 3.0 A. This suggests that many of the type I' turns in X-ray structures may be adopted due to crystal packing effects.  相似文献   

16.
    
A peptide-plane flip is a large-scale rotation of the peptide plane that takes the phi,psi angles at residues i and i + 1 to different structural regions in the Ramachandran plot with a comparatively small effect on the relative orientation of their side chains. This phenomenon, which is expected to play an important role during the early stages of protein folding, has been investigated using 76 proteins for which two high-resolution X-ray conformations are available. Peptide-plane flips are identified by looking for those cases where changes in /psi(i)/ + /phi(i + 1)/ are large (>200 degrees), but changes in /psi(i) + phi(i + 1)/ are comparatively small (<50 degrees). Of a total of 23 cases, the most common peptide-plane flip was identified to be the type I to type II beta-turn interconversion. Although individually rarer, there are many other types of flips that are collectively more common. Given the four main accessible regions alpha(R), alpha(L), beta and epsilon, identified from the phi,psi distribution corresponding to non-hydrogen-bonded peptide planes, 32 main types of peptide-plane flip are identified. Only 8 of these are \"passive,\" in that they require only relatively minor adjustments in the orientation of adjacent peptide planes. Of these, only the type I to type II beta-turn interconversion, denoted, beta(i) + alpha(L)(i + 1) <--> alpha(R)(i) + alpha(R)(i + 1), and the rarer alpha(R)(i) + alpha(L)(i + 1) <--> beta(i) + alpha(R)(i + 1), do not involve the epsilon region. \"Active\" peptide-plane flips affect the orientation of adjacent peptide planes. The flip, alpha(L)(i) + alpha(L)(i + 1) <--> beta(i) + beta(i + 1), of which one example was found, shows how concerted peptide-plane flips can convert the alpha(L) structure to the beta structure without affecting the relative orientations of the side chains.  相似文献   

17.
    
Methods that predict the topology of helical membrane proteins are standard tools when analyzing any proteome. Therefore, it is important to improve the performance of such methods. Here we introduce a novel method, PRODIV-TMHMM, which is a profile-based hidden Markov model (HMM) that also incorporates the best features of earlier HMM methods. In our tests, PRODIV-TMHMM outperforms earlier methods both when evaluated on \"low-resolution\" topology data and on high-resolution 3D structures. The results presented here indicate that the topology could be correctly predicted for approximately two-thirds of all membrane proteins using PRODIV-TMHMM. The importance of evolutionary information for topology prediction is emphasized by the fact that compared with using single sequences, the performance of PRODIV-TMHMM (as well as two other methods) is increased by approximately 10 percentage units by the use of homologous sequences. On a more general level, we also show that HMM-based (or similar) methods perform superiorly to methods that focus mainly on identification of the membrane regions.  相似文献   

18.
BET3 is a component of TRAPP, a complex involved in the tethering of transport vesicles to the cis-Golgi membrane. The crystal structure of human BET3 has been determined to 1.55-A resolution. BET3 adopts an alpha/beta-plait fold and forms dimers in the crystal and in solution, which predetermines the architecture of TRAPP where subunits are present in equimolar stoichiometry. A hydrophobic pocket within BET3 buries a palmitate bound through a thioester linkage to cysteine 68. BET3 and yeast Bet3p are palmitoylated in recombinant yeast cells, the mutant proteins BET3 C68S and Bet3p C80S remain unmodified. Both BET3 and BET3 C68S are found in membrane and cytosolic fractions of these cells; in membrane extractions, they behave like tightly membrane-associated proteins. In a deletion strain, both Bet3p and Bet3p C80S rescue cell viability. Thus, palmitoylation is neither required for viability nor sufficient for membrane association of BET3, which may depend on protein-protein contacts within TRAPP or additional, yet unidentified modifications of BET3. A conformational change may facilitate palmitoyl extrusion from BET3 and allow the fatty acid chain to engage in intermolecular hydrophobic interactions.  相似文献   

19.
    
Penicillin-binding proteins (PBPs) catalyze the final stages of bacterial cell wall biosynthesis. PBPs form stable covalent complexes with beta-lactam antibiotics, leading to PBP inactivation and ultimately cell death. To understand more clearly how PBPs recognize beta-lactam antibiotics, it is important to know their energies of interaction. Because beta-lactam antibiotics bind covalently to PBPs, these energies are difficult to measure through binding equilibria. However, the noncovalent interaction energies between beta-lactam antibiotics and a PBP can be determined through reversible denaturation of enzyme-antibiotic complexes. Escherichia coli PBP 5, a D-alanine carboxypeptidase, was reversibly denatured by temperature in an apparently two-state manner with a temperature of melting (T(m)) of 48.5 degrees C and a van't Hoff enthalpy of unfolding (H(VH)) of 193 kcal/mole. The binding of the beta-lactam antibiotics cefoxitin, cloxacillin, moxalactam, and imipenem all stabilized the enzyme significantly, with T(m) values as high as +4.6 degrees C (a noncovalent interaction energy of +2.7 kcal/mole). Interestingly, the noncovalent interaction energies of these ligands did not correlate with their second-order acylation rate constants (k(2)/K'). These rate constants indicate the potency of a covalent inhibitor, but they appear to have little to do with interactions within covalent complexes, which is the state of the enzyme often used for structure-based inhibitor design.  相似文献   

20.
    
Among the many PWWP-containing proteins, the largest group of homologous proteins is related to hepatoma-derived growth factor (HDGF). Within a well-conserved region at the extreme N-terminus, HDGF and five HDGF-related proteins (HRPs) always have a PWWP domain, which is a module found in many chromatin-associated proteins. In this study, we determined the solution structure of the PWWP domain of HDGF-related protein-3 (HRP-3) by NMR spectroscopy. The structure consists of a five-stranded beta-barrel with a PWWP-specific long loop connecting beta2 and beta3 (PR-loop), followed by a helical region including two alpha-helices. Its structure was found to have a characteristic solvent-exposed hydrophobic cavity, which is composed of an abundance of aromatic residues in the beta1/beta2 loop (beta-beta arch) and the beta3/beta4 loop. A similar ligand binding cavity occurs at the corresponding position in the Tudor, chromo, and MBT domains, which have structural and probable evolutionary relationships with PWWP domains. These findings suggest that the PWWP domains of the HDGF family bind to some component of chromatin via the cavity.  相似文献   

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