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Biomedical subjects

M Sax

Publications and source records attributed to M Sax.

At least 19 recordsLinked to original sources
PubMed1992

Crystal structure of staphylococcal enterotoxin B, a superantigen.

The three-dimensional structure of staphylococcal enterotoxin B, which is both a toxin and a super-antigen, has been determined to a resolution of 2.5 A. The unusual main-chain fold containing two domains may represent a general motif adopted by all staphylococcal enterotoxins. The T-cell receptor binding site encompasses a shallow cavity formed by both domains. The MHCII molecule binds to an adjacent site. Another cavity with possible biological activity was also identified.

Animals↗
PubMed1992

Refined structure of rat Clara cell 17 kDa protein at 3.0 A resolution.

The rat Clara cell 17 kDa protein (previously referred to as the rat Clara cell 10 kDa protein) has been reported to inhibit phospholipase A2 and papain, and to also bind progesterone. It has been isolated from rat lung lavage fluid and crystallized in the space group P6(5)22. The structure has been determined to 3.0 A resolution using the molecular replacement method. Uteroglobin, whose amino acid sequence is 55.7% identical, was used as the search model. The structure was then refined using restrained least-squares and simulated annealing methods. The R-factor is 22.5%. The protein is a covalently bound dimer. Two disulfide bonds join the monomers together in an antiparallel manner such that the dimer encloses a large internal hydrophobic cavity. The hydrophobic cavity is large enough to serve as the progesterone binding site, but access to the cavity is limited. Each monomer is composed of four alpha-helices. The main-chain structure of the Clara cell protein closely resembles that of uteroglobin, but the nature of many of the exposed side-chains differ. This is true, particularly in a hypervariable region between residues 23 and 36, and in the H1H4 pocket.

Amino Acid Sequence↗
PubMed1991

Crystal structure of a bovine neurophysin II dipeptide complex at 2.8 A determined from the single-wavelength anomalous scattering signal of an incorporated iodine atom.

The crystal structure of a dipeptide complex of bovine neurophysin II has been solved at 2.8 A resolution solely by using single-wavelength anomalous scattering data from a single iodinated derivative. The asymmetric unit is an elongated tetramer of dimensions 110 x 40 x 30 A, composed of two dimers related by pseudo twofold symmetry. Each monomer consists of two homologous layers, each with four antiparallel beta-strands. The two regions are connected by a helix followed by a long loop. Monomer-monomer contacts involve antiparallel beta-sheet interactions, which form a dimer with two layers of eight beta-strands. One peptide per monomer occupies the principal hormone-binding pocket formed by part of the amino-terminal region and parts of the connecting helix and loop, with binding to protein consistent with conclusions drawn from solution studies. Dimer-dimer contacts involve the Tyr49 region adjacent to this site. A fifth dipeptide, of unknown biological significance, helps to stabilize one of the monomer-monomer interfaces and the tetramer-tetramer network in the crystal.

Amino Acid Sequence↗
PubMed1990

Preliminary crystallographic data for the thiamin diphosphate-dependent enzyme pyruvate decarboxylase from brewers' yeast.

Single crystals of the thiamin diphosphate (the vitamin B1 coenzyme)-dependent enzyme pyruvate decarboxylase (EC 4.1.1.1) from brewers' yeast have been grown using polyethylene glycol as a precipitating agent. Crystals of the homotetrameric version alpha 4 of the holoenzyme are triclinic, space group P1, with cell constants a = 81.0, b = 82.4, c = 116.6 A, alpha = 69.5 beta = 72.6, gamma = 62.4 degrees. The crystals are reasonably stable in a rotating anode x-ray beam and diffract to at least 2.5 A resolution. The Vm value of 2.55 A/dalton is consistent with a unit cell containing four subunits with mass of approximately 60 kDa each. Rotation function results with native data indicate strong non-crystallographic 222 symmetry relating the four identical subunits, thus density averaging methods are likely to play a role in the structure determination.

Macromolecular Substances↗
PubMed1990

Direct methods with single isomorphous replacement data. I. Reduction of systematic errors.

The direct-methods procedure for single isomorphous replacement (SIR) data [Hauptman (1982). Acta Cryst. A38, 289-294], as modified by Fortier, Moore & Fraser [Acta Cryst. (1985), A41, 571-577] has been implemented and tested with a large number of known structures. It was found that the modified procedure greatly reduces the bias toward 'unresolved' SIR invariant values associated with estimates of 0 or pi, but does not remove it entirely. If the heavy atoms are not in a centrosymmetric array the centroid of the distribution of invariant estimates is not centered on true protein values, but is biased toward conventional SIR values by up to 15 degrees, thus errors in the estimates are not random but systematic. When the heavy atoms are in a centrosymmetric array (or single heavy-atom site in space group P21), the distribution of estimates is often sharply bimodal, with peaks centered at both true invariant values and pure 'unresolved' SIR values. Simple procedures are given which can be applied in both situations to reduce significantly the bias with no overall loss of accuracy. An additional correction factor is then described which can be used to remove nearly all of the bias, and improve the accuracy as well. The result is that errors in the corrected invariant estimates are small in magnitude, but are now also random instead of systematic. Since the number of estimates greatly exceeds the number of phases, the remaining random errors should have little impact in phasing processes.

Bence Jones Protein↗
PubMed1990

Free-solution isoelectric focusing for the purification of Staphylococcus aureus enterotoxin C1.

A free-solution isoelectric focusing protocol was developed for the preparative purification of Staphylococcus aureus enterotoxin C1 (SEC1). A toxin consisting of a single isoelectric species, pI 8.8, was purified. Thirty-nine milligrams of SEC1 was recovered from 3 liters of culture supernatant. This significantly improved purification scheme utilized ammonium sulfate precipitation and the Bio-Rad Rotofor isoelectric cell to complete isolation in 2 days, thereby avoiding the protein degradation prevalent when published procedures are used. The purification protocol developed here for SEC1 is used to illustrate the utility of Rotofor fractionation in the general purification of bacterial exotoxins.

Ammonium Sulfate↗
PubMed1989

A new crystal form of ricin-OR.

Ricin-OR, an antitumor toxin, has been crystallized in space group P2 with cell parameters a = 8.77 nm, b = 4.64 nm, c = 7.64 nm and beta = 101 degrees. There is one molecule in the asymmetric unit and the solvent content is estimated to be 48% by volume. The crystals diffract to 0.25 nm resolution which is higher than that of the previously reported C2 crystal form which had a solvent content of 65%.

Antineoplastic Agents↗
PubMed1988

Crystal structure of an antifreeze polypeptide and its mechanistic implications.

The X-ray crystallographic structure of an antifreeze polypeptide from the fish winter flounder, has been determined at 2.5 A by an analysis of the Patterson function. This is the first report of a polypeptide of this size that is a single alpha-helix. A proposed mechanism of antifreeze binding to ice surfaces is given which requires: first, that the dipole moment from the helical structure dictates the preferential alignment of the peptide to the c-axis of ice nuclei; second, amphiphilicity of the helix; and third, torsional freedom of the side chains to facilitate hydrogen bonding to ice surfaces.

Amino Acid Sequence↗
PubMed1988

Crystals of modified bovine neurophysin II.

An enzymatically modified form of bovine neurophysin II has been crystallized in three unique crystal forms. The orthorhombic form crystallizes in space group P2(1)2(1)2 with a = 15.33 nm, b = 6.92 nm, c = 3.63 nm, with four molecules in the asymmetric unit. The monoclinic form crystallizes in space group P2(1) with a = 6.22 nm, b = 9.55 nm, c = 5.45 nm and beta = 110.2 degrees, with eight molecules in the asymmetric unit. The tetragonal form crystallizes in space group P4(1)2(1)2 or P4(3)2(1)2 with a = 14.1 nm and c = 14.2 nm, with twelve molecules in the asymmetric unit. We report here the crystallization conditions, as well as the crystal data.

Animals↗