Biomedical subjects

In-Ja L Byeon

Publications and source records attributed to In-Ja L Byeon.

8 recordsLinked to original sources

PubMed2005

Structural consequences of the pH-induced conformational switch in A.polyphemus pheromone-binding protein: mechanisms of ligand release.

Olfaction in moths is one of the most impressive examples of chemical communication found in nature for its exquisite sensitivity and selectivity. Pheromone-binding proteins (PBPs), present in the antennae of male moth and other insect species, bind the hydrophobic pheromone molecules and transport them to the G protein-coupled olfactory receptor proteins. The targeted delivery of these non-polar ligands to membrane-bound receptors involves ligand release on or near the target cell membranes, the molecular details of which are still not well understood. The PBP from the giant silk moth Antheraea polyphemus (ApolPBP) binds acetate pheromone only at pH above 6.0, and its structure at pH 6.3 has been determined previously. Here we report the solution NMR structure of ApolPBP at the acidic pH 5.2. Comparison of the present structure to that at neutral pH reveals the details of the pH-induced conformational changes and provides mechanistic clues for ligand release at acidic pH. The ApolPBP pH-induced structural change is quite different from that observed for alcohol binding Bombyx mori PBP (BmorPBP), where the C-terminal segment folds into a helix and occupies the ligand binding cavity. We observe a reorientation of helices alpha1, alpha3, and alpha4 at acidic pH caused by protonation of His69, His70 and His95 in the interior. This provides the driving force behind the opening of the ligand binding cavity and the release of the pheromone molecule from its carrier protein near the membrane.

Amino Acid Sequence↗

PubMed2005

The GB1 amyloid fibril: recruitment of the peripheral beta-strands of the domain swapped dimer into the polymeric interface.

Three-dimensional domain swapping has been evoked as a mechanism for oligomerization of proteins. Here, we show for the immunoglobulin-binding domain B1 of streptococcal protein G (GB1) that fibril formation is observed readily for variants that exist as domain-swapped dimers. No fibril was formed by a revertant that exhibits the stable wild-type GB1 fold or a mutant comprising a highly destabilized, fluctuating ensemble of conformers. Structural features of the GB1 amyloid fibril were characterized by cysteine disulfide cross-linking. Residues in the outer edge beta-strands of the domain-swapped dimer readily form intermolecular disulfide bonds prior to and during fibril formation. On the basis of these data, a structural model for the assembly of domain-swapped dimers into a polymeric structure of the GB1 fibril is proposed.

Amyloid↗

PubMed2005

Sequential phosphorylation and multisite interactions characterize specific target recognition by the FHA domain of Ki67.

The forkhead-associated (FHA) domain of human Ki67 interacts with the human nucleolar protein hNIFK, recognizing a 44-residue fragment, hNIFK226-269, phosphorylated at Thr234. Here we show that high-affinity binding requires sequential phosphorylation by two kinases, CDK1 and GSK3, yielding pThr238, pThr234 and pSer230. We have determined the solution structure of Ki67FHA in complex with the triply phosphorylated peptide hNIFK226-269(3P), revealing not only local recognition of pThr234 but also the extension of the beta-sheet of the FHA domain by the addition of a beta-strand of hNIFK. The structure of an FHA domain in complex with a biologically relevant binding partner provides insights into ligand specificity and potentially links the cancer marker protein Ki67 to a signaling pathway associated with cell fate specification.

CDC2 Protein Kinase↗

PubMed2004

Solution structure of the human oncogenic protein gankyrin containing seven ankyrin repeats and analysis of its structure--function relationship.

Human gankyrin (226 residues, 24.4 kDa) is a liver oncoprotein that plays an important role in the development of human hepatocellular carcinomas. In this paper, its solution structure is reported, which is the largest ankyrin protein ever determined by NMR. The highly degenerate primary sequences of the seven ankyrin repeats presented a major challenge, which was overcome by combined use of TROSY experiments, perdeuterated samples, isotope-filtered NMR experiments, and residual dipolar couplings. The final structure was of high quality, with atomic rmsds for the backbone (N, C', and C(alpha)) and all heavy atoms (residues 4-224) of 0.69 +/- 0.09 and 1.04 +/- 0.09 A, respectively. Detailed analyses of NMR data suggested that the conserved TPLH motifs play important structural roles in stabilizing the repeating ankyrin scaffold. Gankyrin is conformationally more stable than the tumor suppressor p16(INK4A), possibly due to the structural roles of conserved residues evidenced by slowly exchanging backbone amides as well as hydrogen bonding networks involving labile side chain protons. Structural comparison with p16(INK4A) identified several residues of gankyrin that are potentially important for CDK4 binding, whereas observation of the thiol proton of C180 indicated a well-structured Rb-binding site in the helical region of the sixth ankyrin repeat. Interestingly, the CDK4-binding site and Rb-binding site located in N- and C-terminal regions, respectively, are separated by comparatively more stable ankyrin repeats and highly condensed positive surface charge. These results and analyses will shed light on the structural basis of the function of human gankyrin.

Amino Acid Sequence↗

PubMed2004

A captured folding intermediate involved in dimerization and domain-swapping of GB1.

Immunoglobulin binding domain B1 of streptococcal protein G (GB1), a small (56 residues), stable, single domain protein, is one of the most extensively used model systems in the area of protein folding and design. The recently determined NMR structure of a quadruple mutant (HS#124F26A, L5V/F30V/Y33F/A34F) revealed a domain-swapped dimer that dissociated into a partially folded, monomeric species at low micromolar protein concentrations. Here, we have characterized this monomeric, partially folded species by NMR and show that extensive conformational heterogeneity for a substantial portion of the polypeptide chain exists. Exchange between the conformers within the monomer ensemble on the microsecond to millisecond timescale renders the majority of backbone amide resonances broadened beyond detection. Despite these extensive temporal and spatial fluctuations, the overall architecture of the monomeric mutant protein resembles that of wild-type GB1 and not the monomer unit of the domain-swapped dimer.

Amino Acid Sequence↗

PubMed2004

The ligand specificity of yeast Rad53 FHA domains at the +3 position is determined by nonconserved residues.

On the basis of the results from our laboratory and others, we recently suggested that the ligand specificity of forkhead-associated (FHA) domains is controlled by variations in three major factors: (i) residues interacting with pThr, (ii) residues recognizing the +1 to +3 residues from pThr, and (iii) an extended binding surface. While the first factor has been well established by several solution and crystal structures of FHA-phosphopeptide complexes, the structural bases of the second and third factors are not well understood and are likely to vary greatly between different FHA domains. In this work, we proposed and tested the hypothesis that nonconserved residues G133 and G135 of FHA1 and I681 and D683 of FHA2, located outside of the core FHA region of yeast Rad53 FHA domains, contribute to the specific recognition of the +3 position of different phosphopeptides. By rational mutagenesis of these residues, the specificity of FHA1 has been changed from predominantly pTXXD to be equally acceptable for pTXXD, pTXXL, and pYXL, which are similar to the specificities of the FHA2 domain of Rad53. Conversely, the +3 position specificity of FHA2 has been engineered to be more like FHA1 with the I681A mutation. These results were based on library screening as well as binding analyses of specific phosphopeptides. Furthermore, results of structural analyses by NMR indicate that some of these residues are also important for the structural integrity of the loops.

Arginine↗

PubMed2004

Solution NMR studies of the A beta(1-40) and A beta(1-42) peptides establish that the Met35 oxidation state affects the mechanism of amyloid formation.

The pathogenesis of Alzheimer's disease is characterized by the aggregation and fibrillation of the 40-residue A beta(1-40) and 42-residue A beta(1-42) peptides into amyloid plaques. The structural changes associated with the conversion of monomeric A beta peptide building blocks into multimeric fibrillar beta-strand aggregates remain unknown. Recently, we established that oxidation of the methionine-35 side chain to the sulfoxide (Met35(red) --> Met35(ox)) significantly impedes the rate of aggregation and fibrillation of the A beta peptide. To explore this effect at greater resolution, we carefully compared the (1)H, (15)N, and (13)C NMR chemical shifts of four A beta peptides that had the Met35 reduced or oxidized (A beta(1-40)Met35(red), A beta(1-40)Met35(ox), A beta(1-42)Met35(red), and A beta(1-42)Met35(ox)). With the use of a special disaggregation protocol, the highly aggregation prone A beta peptides could be studied at higher, millimolar concentrations (as required by NMR) in aqueous solution at neutral pH, remaining largely monomeric at 5 degrees C as determined by sedimentation equilibrium studies. The NOE, amide-NH temperature coefficients, and chemical shift indices of the (1)H alpha, (13)C alpha, and (13)C beta established that the four peptides are largely random, extended chain structures, with the Met35(ox) reducing the propensity for beta-strand structure at two hydrophobic regions (Leu17-Ala21 and Ile31-Val36), and turn- or bendlike structures at Asp7-Glu11 and Phe20-Ser26. Additional NMR studies monitoring changes that occur during aging at 37 degrees C established that, along with a gradual loss of signal/noise, the Met35(ox) significantly hindered upfield chemical shift movements of the 2H NMR signals for the His6, His13, and His14 side chains. Taken together, the present NMR studies demonstrate that the Met35(red) --> Met35(ox) conversion prevents aggregation by reducing both hydrophobic and electrostatic association and that the A beta(1-40)Met35(red), A beta(1-40)Met35(ox), A beta(1-42)Met35(red), and A beta(1-42)Met35(ox) peptides may associate differently, through specific, sharp changes in structure during the initial stages of aggregation.

Amino Acid Sequence↗

PubMed2003

A protein contortionist: core mutations of GB1 that induce dimerization and domain swapping.

Immunoglobulin-binding domain B1 of streptococcal protein G (GB1), a small (56 residues), stable, single-domain protein, is one of the most extensively used model systems in the area of protein folding and design. Recently, NMR and X-ray structures of a quintuple GB1 core mutant (L5V/A26F/F30V/Y33F/A34F) that showed an unexpected, intertwined tetrameric architecture were determined. Here, we report the NMR structure of another mutant, derived from the tetramer by reverting the single amino acid position F26 back to the wild-type sequence A26. The structure reveals a domain-swapped dimer that involves exchange of the second beta-hairpin. The resulting overall structure comprises an eight-stranded beta-sheet whose concave side is covered by two alpha helices. The dimer dissociates into a partially folded, monomeric species with a dissociation constant of 93(+/-10)microM.

Amino Acid Sequence↗