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Padmanabhan Balaram

Publications and source records attributed to Padmanabhan Balaram.

40 records · Page 3Linked to original sources
PubMed2002

Design and construction of an open multistranded beta-sheet polypeptide stabilized by a disulfide bridge.

The design and characterization of an open eight-stranded beta-sheet in a synthetic, 2-fold symmetric 70-residue peptide is described. The design strategy involves the generation of a 35-residue four-stranded beta-sheet peptide in which successive hairpins are nucleated by appropriately positioned (D)Pro-Xxx sequences. Oxidative dimerization using a single Cys residue positioned at the center of the C-terminal strand results in a disulfide-bridged eight-stranded structure. Nuclear Overhauser effects firmly establish an eight-stranded beta-sheet in methanol. In water, the outer strands are frayed, but a well-defined four-stranded beta-sheet stabilized by a disulfide bridge and a hydrophobic cluster is determined from NMR data. Comparison of the precursor peptide with the disulfide-bridged dimer reveals considerable enhancement of beta-sheet content in the latter, suggesting that the disulfide cross-link is an effective strategy for the stabilization of beta-sheets.

Amino Acid Motifs↗
PubMed2002

Inhibition of plasmodium falciparum triose-phosphate isomerase by chemical modification of an interface cysteine. Electrospray ionization mass spectrometric analysis of differential cysteine reactivities.

Plasmodium falciparum triose-phosphate isomerase, a homodimeric enzyme, contains four cysteine residues at positions 13, 126, 196, and 217 per subunit. Among these, Cys-13 is present at the dimer interface and is replaced by methionine in the corresponding human enzyme. We have investigated the effect of sulfhydryl labeling on the parasite enzyme, with a view toward developing selective covalent inhibitors by targeting the interface cysteine residue. Differential labeling of the cysteine residues by iodoacetic acid and iodoacetamide has been followed by electrospray ionization mass spectrometry and positions of the labels determined by analysis of tryptic fragments. The rates of labeling follows the order Cys-196 > Cys-13 Cys-217/Cys-126, which correlates well with surface accessibility calculations based on the enzyme crystal structure. Iodoacetic acid labeling leads to a soluble, largely inactive enzyme, whereas IAM labeling leads to precipitation. Carboxyl methylation of Cys-13 results in formation of monomeric species detectable by gel filtration. Studies with an engineered C13D mutant permitted elucidation of the effects of introducing a negative charge at the interface. The C13D mutant exhibits a reduced stability to denaturants and 7-fold reduction in the enzymatic activity even under the concentrations in which dimeric species are observed.

Amino Acid Sequence↗
PubMed2002

Infinite pleated beta -sheet formed by the beta-hairpin Boc-beta-Phe-beta-Phe-D-Pro-Gly-beta-Phe-beta-Phe-OMe.

A beta-hairpin conformation and extended beta-pleated sheet assembly have been characterized by single crystal x-ray diffraction for the synthetic peptide t-butoxycarbonyl--beta-Phe-beta-Phe-D-Pro-Gly-beta-Phe-beta-Phe-methyl ester [beta-Phe: (S)-beta(3) homophenylalanine]. The centrally located D-Pro-Gly segment nucleates a chain reversal in a type II' beta-turn conformation. Two intramolecular cross-strand hydrogen bonds stabilize the peptide fold. Intermolecular NH...O[double bond]C hydrogen bonds (two on each side of the hairpin) connect the hairpins into an infinitely extended beta-sheet. The beta-residues cause all C[double bond]O groups to point in the same direction, resulting in a "polar" sheet by the unidirectional alignment of NH...O[double bond]C hydrogen bonds. In contrast, beta-sheets formed by alpha-residues have alternating directions for the hydrogen bonds, thus resulting in an "apolar" sheet. The crystallographic parameters for C(53)H(66)N(6)O(9) x CH(3)OH are: space group P2(1), a = 9.854(2) A, b = 10.643(2) A, c = 25.296(4) A, beta = 100.39(2) degrees, Z = 2, agreement factor R(1) = 0.065 for 3,706 data observed >4 sigma(F) and a resolution of 0.90 A.

Amino Acids↗