[Show abstract][Hide abstract] ABSTRACT: Profilin is a ubiquitous eukaryotic protein that binds to both cytosolic actin and the phospholipid phospha-tidylinositol-4,5-bisphosphate. These dual competitive binding capabilities of profilin suggest that profilin serves as a link between the phosphatidyl inositol cycle and actin polymerization, and thus profilin may be an essential component in the signaling pathway leading to cytoskeletal rearrangement.
The refined three-dimensional solution structure of human profilin I has been determined using multidimensional heteronuclear NMR spectroscopy. Twenty structures were selected to represent the solution conformational ensemble. This ensemble of structures has root-mean-square distance deviations from the mean structure of 0.58 Å for the backbone atoms and 0.98 Å for all non-hydrogen atoms. Comparison of the solution structure of human profilin to the crystal structure of bovine profilin reveals that, although profilin adopts essentially identical conformations in both states, the solution structure is more compact than the crystal structure. Interestingly, the regions that show the most structural diversity are located at or near the actin-binding site of profilin. We suggest that structural differences are reflective of dynamical properties of profilin that facilitate favorable interactions with actin. The global folding pattern of human profilin also closely resembles that of Acanthamoeba profilin I, reflective of the 22% sequence identity and ∼45% sequence similarity between these two proteins.
Protein Science 03/2008; 4(3):450-9. DOI:10.1002/pro.5560040312 · 2.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The NMR structure is presented for compound 1 (BMS-480404) (Ki = 33 (+/-2) nM) bound to keratinocyte fatty acid-binding protein. This article describes interactions between a high affinity drug-like compound and a member of the fatty acid-binding protein family. A benzyl group ortho to the mandelic acid in 1 occupies an area of the protein that fatty acids do not normally contact. Similar to that in the kFABP-palmitic acid structure, the acid moiety in 1 is proximal to R129 and Y131. Computational modeling indicates that the acid moiety in 1 interacts indirectly via a modeled water molecule to R109.
[Show abstract][Hide abstract] ABSTRACT: CFE88 is a conserved essential gene product from Streptococcus pneumoniae. This 227-residue protein has minimal sequence similarity to proteins of known 3D structure. Sequence alignment models and computational protein threading studies suggest that CFE88 is a methyltransferase. Characterization of the conformation and function of CFE88 has been performed by using several techniques. Backbone atom and limited side-chain atom NMR resonance assignments have been obtained. The data indicate that CFE88 has two domains: an N-terminal domain with 163 residues and a C-terminal domain with 64 residues. The C-terminal domain is primarily helical, while the N-terminal domain has a mixed helical/extended (Rossmann) fold. By aligning the experimentally observed elements of secondary structure, an initial unrefined model of CFE88 has been constructed based on the X-ray structure of ErmC' methyltransferase (Protein Data Bank entry 1QAN). NMR and biophysical studies demonstrate binding of S-adenosyl-L-homocysteine (SAH) to CFE88; these interactions have been localized by NMR to the predicted active site in the N-terminal domain. Mutants that target this predicted active site (H26W, E46R, and E46W) have been constructed and characterized. Overall, our results both indicate that CFE88 is a methyltransferase and further suggest that the methyltransferase activity is essential for bacterial survival.
Protein Science 07/2005; 14(6):1472-84. DOI:10.1110/ps.051389605 · 2.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Adipocyte lipid-binding protein (A-LBP) and muscle fatty acid-binding protein (M-FABP) are members of a family of small ( approximately 15 kDa) cytosolic proteins that are involved in the metabolism of fatty acids and other lipid-soluble molecules. Although highly homologous (65%) and structurally very similar, A-LBP and M-FABP display distinct ligand binding characteristics. Since ligand binding may be influenced by intrinsic protein dynamical properties, we have characterized the backbone and side chain dynamics of uncomplexed (apo) human A-LBP and M-FABP. Backbone dynamics were characterized by measurements of 15N T1 and T2 values and ¿1H¿-15N NOEs. These data were analyzed using model-free spectral density functions and reduced spectral density mapping. The dynamics of methyl-containing side chains were charaterized by measurements of 2H T1 and T1rho relaxation times of 13C1H22H groups. The 2H relaxation data were analyzed using the model-free approach. For A-LBP, 15N relaxation data were obtained for 111 residues and 2H relaxation data were obtained for 42 methyl groups. For M-FABP, 15N relaxation data were obtained for 111 residues and 2H relaxation data were obtained for 53 methyl groups. The intrinsic flexibilities of these two proteins are compared, with particular emphasis placed on binding pocket residues. There are a number of distinct dynamical differences among corresponding residues between the two proteins. In particular, many residues display greater backbone picosecond to nanosecond and/or microsecond to millisecond time scale mobility in A-LBP relative to M-FABP, including F57, K58, and most residues in alpha-helix 2 (residues 28-35). Variations in the dynamics of this region may play a role in ligand selectivity. The side chains lining the fatty acid binding pocket display a wide range of motional restriction in both proteins. Side chains showing distinct dynamical differences between the two proteins include those of residues 20, 29, and 51. This information provides a necessary benchmark for determining dynamical changes induced by ligand binding and may ultimately lead to an enhanced understanding of ligand affinity and selectivity among fatty acid-binding proteins.
[Show abstract][Hide abstract] ABSTRACT: Backbone-atom resonances have been assigned for both the substrate-free and the NADP+-complexed forms of UDP-N-acetylenolpyruvylglucosamine reductase (MurB), a monomeric, 347-residue (38.5 kDa) flavoenzyme essential for bacterial cell-wall biosynthesis. NMR studies were performed using perdeuterated, uniformly 13C/15N-labeled samples of MurB. In the case of substrate-free MurB, one or more backbone atoms have been assigned for 334 residues (96%). The assigned backbone atoms include 309 1HN and 15N atoms (94%), 315 13CO atoms (91%), 331 13C(alpha) atoms (95%), and 297 13C(beta) atoms (93%). For NADP+-complexed MurB, one or more backbone atoms have been assigned for 313 residues (90%); these include 283 1HN and 15N atoms (86%), 305 13CO atoms (88%), 310 13C(alpha) atoms (89%), and 269 13C(beta) atoms (84%). The strategies used for obtaining resonance assignments are described in detail. Information on the secondary structure in solution for both the substrate-free and NADP+-complexed forms of the enzyme has been derived both from 13C(alpha) and 13C(beta) chemical-shift deviations from random-coil values and from 1HN-1HN NOEs. These data are compared to X-ray crystallographic structures of substrate-free MurB and MurB complexed with the UDP-N-acetylglucosamine enolpyruvate (UNAGEP) substrate. NADP+ binding induces significant chemical-shift changes in residues both within the known UNAGEP and FAD binding pockets and within regions known to undergo conformational changes upon UNAGEP binding. The NMR data indicate that NADP+ and UNAGEP utilize the same binding pocket and, furthermore, that the binding of NADP+ induces structural changes in MurB. Finally, many of the residues within the UNAGEP/NADP+ binding pocket were difficult to assign due to dynamic processes which weaken and/or broaden the respective resonances. Overall, our results are consistent with MurB having a flexible active site.
[Show abstract][Hide abstract] ABSTRACT: Perdeuteration of all non-exchangeable proton sites can significantly increase the size of proteins and protein complexes for which NMR resonance assignments and structural studies are possible. Backbone 1H, 15N, 13CO, 13C alpha and 13C beta chemical shifts and aliphatic side-chain 13C and 1H(N)/15N chemical shifts for human carbonic anhydrase II (HCA II), a 259 residue 29 kDa metalloenzyme, have been determined using a strategy based on 2D, 3D and 4D heteronuclear NMR experiments, and on perdeuterated 13C/15N-labeled protein. To date, HCA II is one of the largest monomeric proteins studied in detail by high-resolution NMR. Of the backbone resonances, 85% have been assigned using fully protonated 15N and 3C/15N-labeled protein in conjunction with established procedures based on now standard 2D and 3D NMR experiments. HCA II has been perdeuterated both to complete the backbone resonance assignment and to assign the aliphatic side-chain 13C and 1H(N)/15N resonances. The incorporation of 2H into HCA II dramatically decreases the rate of 13C and 1H(N)T2 relaxation. This, in turn, increases the sensitivity of several key 1H/13C/15N triple-resonance correlation experiments. Many otherwise marginal heteronuclear 3D and 4D correlation experiments, which are important to the assignment strategy detailed herein, can now be executed successfully on HCA II. Further analysis suggests that, from the perspective of sensitivity, perdeuteration should allow other proteins with rotational correlation times significantly longer than HCA II (tau c = 11.4 ns) to be studied successfully with these experiments. Two different protocols have been used to characterize the secondary structure of HCA II from backbone chemical-shift data. Secondary structural elements determined in this manner compare favorably with those elements determined from a consensus analysis of the HCA II crystal structure. Finally, having outlined a general strategy for assigning backbone and side-chain resonances in a perdeuterated large protein, we propose a strategy whereby this information can be used to glean more detailed structural information from the partially or fully protonated protein equivalent.
[Show abstract][Hide abstract] ABSTRACT: Signal transduction in B cells is mediated, in part, by the interaction of the cytoplasmic components of the antigen receptor complex and various members of the src family tyrosine kinases. Key to this process appears to be the interaction of the tyrosine kinase SH2 domains with the tyrosine-phosphorylated cytoplasmic domain of Ig-alpha, a disulfide-bonded heterodimeric (with Ig-beta or Ig-gamma) transmembrane protein that noncovalently associates with the antigen receptor immunoglobin chains. In addition to binding to the phosphorylated cytoplasmic domains of Ig-alpha and Ig-beta, blk and fyn(T), two members of the src family kinases, have been shown to bind overlapping but distinct sets of phosphoproteins [Malek & Desiderio (1993) J. Biol. Chem. 268. 22557-22565]. A comparison of their three-dimensional structures may elucidate the apparently subtle differences required for phosphoprotein discrimination. To begin characterizing the blk/fyn/phosphosphoprotein interactions, we have determined the three-dimensional solution structure of the SH2 domain of blk kinase by nuclear magnetic resonance (NMR) spectroscopy. 1H, 13C, and 15N resonances of the SH2 domain of blk kinase were assigned by analysis of multidimensional, double- and triple-resonance NMR experiments. Twenty structures of the blk SH2 domain were refined with the program X-PLOR using a total of 2080 experimentally derived conformational restraints. The structures converged to a root-mean-squared (rms) distance deviation of 0.51 and 0.95 A for the backbone atoms and for the non-hydrogen atoms, respectively. The blk SH2 domain adopts the prototypical SH2 fold. Structurally, blk SH2 is most similar to the crystal structure of the v-src SH2 domain [Waksman et al. (1993) Nature 358.646-653] and superimposes on the crystal structure with an rmsd of 1.52 A for the backbone atoms. The largest deviations occur in the four loops interconnecting beta-strands A-E, which are the least well-defined regions in the NMR structure. Exclusion of these loops lowers this rmsd to 0.82 A. The conformation of the BC loop in the blk SH2 domain is similar to the open conformation in the apo lck SH2 domain, suggesting that, like the lck SH2 domain, the blk SH2 domain may have a gated phosphopeptide binding site. Finally, it is proposed that the amino acid substitution of Lys 88 (blk) for Glu [fyn(T)] is important for the observed differences in specificity between blk and fyn(T) SH2 domains.
[Show abstract][Hide abstract] ABSTRACT: The perdeuteration of aliphatic sites in large proteins has been shown to greatly facilitate the process of sequential backbone and side-chain 13C assignments and has also been utilized in obtaining long-range NOE distance restraints for structure calculations. To obtain the maximum information from a 4D 15N/15N-separated NOESY, as many main-chain and side-chain 1HN/15N resonances as possible must be assigned. Traditionally, only backbone amide 1HN/15N resonances are assigned by correlation experiments, whereas slowly exchanging side-chain amide, amino, and guanidino protons are assigned by NOEs to side-chain aliphatic protons. In a perdeuterated protein, however, there is a minimal number of such protons. We have therefore developed several gradient-enhanced and sensitivity-enhanced pulse sequences, containing water-flipback pulses, to provide through-bond correlations of the aliphatic side-chain 1HN/15N resonances to side-chain 13C resonances with high sensitivity: NH2-filtered 2D 1H-15N HSQC(H2N-HSQC), 3D H2N(CO)C gamma/beta and 3D H2N(COC gamma/beta)C beta/alpha for glutamine and asparagine side-chain amide groups; 2D refocused H(N epsilon/zeta)C delta/epsilon and H(N epsilon/zeta C delta/epsilon)C gamma/delta for arginine side-chain amino groups and non-refocused versions for lysine side-chain amino groups; and 2D refocused H(N epsilon)C zeta and nonrefocused H(N epsilon, eta)C zeta for arginine side-chain guanidino groups. These pulse sequences have been applied to perdeuterated 13C-/15N-labeled human carbonic anhydrase II (2H-HCA II). Because more than 95% of all side-chain 13C resonances in 2H-HCA II have already been assigned with the C(CC)(CO)NH experiment, the assignment of the side-chain 1HN/15N resonances has been straightforward using the pulse sequences mentioned above. The importance of assigning these side-chain HN protons has been demonstrated by recent studies in which the calculation of protein global folds was simulated using only 1HN-1HN NOE restraints. In these studies, the inclusion of NOE restraints to side-chain HN protons significantly improved the quality of the global fold that could be determined for a perdeuterated protein [R.A. Venters et al. (1995) J. Am. Chem. Soc., 117, 9592-9593].
[Show abstract][Hide abstract] ABSTRACT: The protein human carbonic anhydrase II (HCA II) has been isotopically labeled with 2H, 13C and 15N for high-resolution NMR assignment studies and pulse sequence development. To increase the sensitivity of several key 1H/13C/15N triple-resonance correlation experiments, 2H has been incorporated into HCA II in order to decrease the rates of 13C and 1HN T2 relaxation. NMR quantities of protein with essentially complete aliphatic 2H incorporation have been obtained by growth of E. coli in defined media containing D2O, [1,2-13C2, 99%] sodium acetate, and [15N, 99%] ammonium chloride. Complete aliphatic deuterium enrichment is optimal for 13C and 15N backbone NMR assignment studies, since the 13C and 1HN T2 relaxation times and, therefore, sensitivity are maximized. In addition, complete aliphatic deuteration increases both resolution and sensitivity by eliminating the differential 2H isotopic shift observed for partially deuterated CHnDm moieties.
[Show abstract][Hide abstract] ABSTRACT: NMR spectroscopy has been used to characterize the protein-protein interactions between the mouse Grb2 (mGrb2) N-terminal SH3 domain complexed with a 15-residue peptide (SPLLPKLPP-KTYKRE) corresponding to residues 1264-1278 of the mouse Sos-2 (mSos-2) protein. Intermolecular interactions between the peptide and 13C-15N-labeled SH3 domain were identified in half-reverse-filtered 2D and 3D NOESY experiments. Assignments for the protons involved in interactions between the peptide and the SH3 domain were confirmed in a series of NOESY experiments using a set of peptides in which different leucine positions were fully deuterated. The peptide ligand-binding site of the mGrb2 N-terminal SH3 domain is defined by the side chains of specific aromatic residues (Tyr7, Phe9, Trp36, Tyr52) that form two hydrophobic subsites contacting the side chains of the peptide Leu4 and Leu7 residues. An adjacent negatively charged subsite on the SH3 surface is likely to interact with the side chain of a basic residue at peptide position 10 that we show to be involved in binding. The peptide-binding site of the SH3 is characterized by large perturbations of amide chemical shifts when the peptide is added to the SH3 domain. The mGrb2 N-terminal SH3 domain structure in the complex is well-defined (backbone RMSD of 0.56 +/- 0.21 calculated over the backbone N, C alpha, and C atoms of residues 1-54). The structure of the peptide in the complex is less well-defined but displays a distinct orientation.(ABSTRACT TRUNCATED AT 250 WORDS)
[Show abstract][Hide abstract] ABSTRACT: The simultaneous acquisition of a 4D gradient-enhanced and sensitivity-enhanced [13C,15N]/[15N,15N]-separated NOESY is presented for the 74-residue [13C,15N]-labeled N-terminal SH3 domain of mGrb2 complexed with a peptide fragment from mSOS-2 in 90% H2O. The method readily accommodates different 13C and 15N spectral widths, but requires that the same number of increments be collected for both 13C and 15N in the simultaneous dimension (F2). For purposes of display and analysis, the two 4D spectra can be deconvolved during the processing stage by the appropriate linear combination of separately stored FIDs. Compared to collecting each of these two 4D data sets separately, the presented method is a factor (2)1/2 more efficient in sensitivity per unit acquisition time. The interleaved nature of this method may also lead to improved peak registration between the two 4D spectra.
[Show abstract][Hide abstract] ABSTRACT: A set of three 3D (1H,13C,15N) triple-resonance correlation experiments has been designed to provide H1'-H8 intraresidue sugar-to-base correlations in purines in an unambiguous and efficient manner. Together, the HsCsNb, HsCs(N)bCb, and HbNbCb experiments correlate the H1' sugar proton to the H8 proton of the attached base by means of the (H1', C1', N9, C8, H8) heteronuclear scalar coupling network. The assignment strategy presented here allows for unambiguous H1'-H8 intraresidue correlations, provided that no two purines have both the same H1' and C1' chemical shifts and the same C8 and N9 chemical shifts. These experiments have yielded H1'-H8 intraresidue sugar-to-base correlations for all five guanosines in the [13C,15N] isotopically labeled RNA duplex r(GGCGCUUGCGUC)2.