Membrane protein extraction and purification using partially-esterified SMA polymers

Styrene maleic acid (SMA) polymers have proven to be very successful for the extraction of membrane proteins, forming SMA lipid particles (SMALPs), which maintain a lipid bilayer around the membrane protein. SMALP-encapsulated membrane proteins can be used for functional and structural studies. The SMALP approach allows retention of important protein-annular lipid interactions, exerts lateral pressure, and offers greater stability than traditional detergent solubilisation. However, SMA polymer does have some limitations, including a sensitivity to divalent cations and low pH, an absorbance spectrum that overlaps with many proteins, and possible restrictions on protein conformational change. Various modified polymers have been developed to try to overcome these challenges, but no clear solution has been found. A series of partially-esterified variants of SMA (SMA 2625, SMA 1440 and SMA 17352) has previously been shown to be highly effective for solubilisation of plant and cyanobacterial thylakoid membranes. It was hypothesised that the partial esterification of maleic acid groups would increase tolerance to divalent cations. Therefore, these partially-esterified polymers were tested for the solubilisation of lipids and membrane proteins, and their tolerance to magnesium ions. It was found that all partially esterified polymers were capable of solubilising and purifying a range of membrane proteins, but the yield of protein was lower with SMA 1440, and the degree of purity was lower for both SMA 1440 and SMA 17352. SMA 2625 performed comparably to SMA 2000. SMA 1440 also showed an increased sensitivity to divalent cations. Thus, it appears the interactions between SMA and divalent cations are more complex than proposed and require further investigation.

Detection of hereditary pyropoikilocytosis by the eosin-5-maleimide (EMA)-binding test is attributable to a marked reduction in EMA-reactive transmembrane proteins

INTRODUCTION

Hereditary spherocytosis (HS) and hereditary pyropoikilocytosis (HPP, severe form of hereditary elliptocytosis) are unrelated red cell disorders caused by defects in distinct regions of the red cell cytoskeleton. The high predictive value of the eosin-5-maleimide (EMA)-binding test for the diagnosis of HS is because of its interaction with transmembrane proteins band 3, Rh protein, Rh glycoprotein and CD47, which are reduced on HS red cells. Our study was undertaken to determine why EMA-labelled HPP red cells were previously found to give much lower fluorescence readings than HS.

METHODS

Flow cytometry was used to determine the relative amounts of monoclonal antibodies bound to red cells from normal adults, HS and HPP groups. Confocal microscopy was used to visualise the overall staining pattern of the red cells with selected antibodies.

RESULTS

In flow cytometry, HPP red cells gave lower antibody binding to the four EMA-reactive membrane proteins than HS red cells and bound less antibody to glycophorins A and C, and CD59. Confocal images of Rh protein and band 3 immunostaining revealed a greater number of HPP red cells having partial or no fluorescence than in HS and normal controls.

CONCLUSION

Lesser amounts of EMA-reactive membrane proteins were detected in HPP than HS red cells, thus confirming their lower fluorescence readings in the EMA-binding test. The concomitant reduction in glycophorins A and C, and CD59 in HPP could have caused cellular contraction, resulting in poikilocytosis.

Toxicity of benzyl cyanide in the rat

Lethal doses of benzyl cyanide in the rat were 0.64 mmol/kg (i.p.), 1.8 and 2.6 mmol/kg (p.o.) for female and male rats, respectively. Sublethal oral doses of benzyl cyanide were nephrotoxic causing increased excretion of protein, amino acids and glucose. Cyanide was slowly liberated from the dosed nitrile and excreted as cyanide and thiocyanate, the proportion of the former increasing with increasing i.p. dose and with the highest oral dose. The oral cyanide antidote was ineffective against benzyl cyanide and the intravenous antidote, Kelocyanor (cobalt edetate), had little beneficial effect.

Technetium Chlorides and Oxochlorides

We have been unable to prepare TcCl6 by the method published previously even though our reaction between Tc and Cl2 gave products which appeared the same. TcO3Cl and TcOCl4 have been prepared and fully characterized for the first time.

Oxochloride Complexes of Rhenium

Attempts to prepare rhenium hexachloride by the method described by Colton (2) have been unsuccessful. The products of the reaction were always impure rhenium oxotetrachloride and rhenium pentachloride. A compound of rhenium(VI), ReOCl4OPCl3, is shown to have a structure analogous to that of rhenium(V) ions [ReOX4.L]− in which the ligands are in a pseudooctahedral arrangement with L trans to the oxo-group (3). Reactions of ReOCl4 and ReOCl4-OPCl3 with pyridine and 2,2′-dipyridyl are described, and a scheme is proposed for the reactions of the products. Two stable complexes of perrhenyl chloride with the above amines have been obtained.

Preparation of β-rhenium tetrachloride

β-Rhenium tetrachloride has been prepared by three different methods. Infrared, magnetic, and X-ray powder diffraction data are reported.

Determination of rhenium: chlorine ratios in complexes by neutron activation

A method is described for the simultaneous determination of rhenium and chlorine in complex compounds. By determining atom ratios, it is unnecessary to weigh samples. The advantages of this method when applied to air-unstable compounds are described.