Analysis of Na+,K+-ATPase by electron microscopy

Changes in Rates of Inpatient Postpartum Long-Acting Reversible Contraception and Sterilization in the USA, 2012-2016

OBJECTIVES

To examine recent rates of long-acting and permanent methods (LAPM) of contraception use during delivery hospitalization and correlates of their use.

METHODS

A retrospective cohort study utilizing the 2012-2016 National Inpatient Sample of hospitalizations in the United States of America. The International Classification of Diseases, 9th and 10th Revision, Clinical Modification codes were used to identify deliveries, inpatient long-acting reversible contraception (IPP LARC), and postpartum tubal ligation (PPTL). We conducted univariable and multivariable logistic regression to examine associations between demographic, clinical, hospital and geographical characteristics with likelihood of LAPM including IPP LARC and PPTL.

RESULTS

Our sample included 3,642,328 unweighted deliveries. The rate of IPP LARC increased from 34.6 to 54.9 per 10,000 deliveries (58.7%), while the rate of PPTL utilization decreased from 719.5 to 671.8 per 10,000 deliveries (6.6%) over the study period. In multivariable analysis of LAPM utilization versus neither, cesarean delivery (aOR 7.25, 95% CI 7.08-7.43) was associated with greater utilization. Native American (aOR 4.01, 95% CI 2.91-5.53) race was associated with increased use of IPP LARC compared to a non-long-acting method of contraception. Age between 18 and 29 years (aOR 6.21, 95% CI 5.42-7.11) was associated with greater use of IPP LARC versus PPTL. Delivering in a rural hospital ((aOR 0.09, 95% CI 0.06-0.12) and cesarean delivery (aOR 0.09, 95% CI 0.06-0.12) were associated with greater use PPTL versus IPP LARC.

CONCLUSIONS

The IPP LARC rate remains at less than 10% the PPTL rates in our study timeframe. The demonstrated variation in uptake of highly effective methods of contraception inpatient after delivery offer possible opportunities for better understanding and improvement in access.

NMR of membrane proteins in micelles and bilayers: the FXYD family proteins

Determining the atomic resolution structures of membrane proteins is of particular interest in contemporary structural biology. Helical membrane proteins constitute one-third of the expressed proteins encoded in a genome, many drugs have membrane-bound proteins as their receptors, and mutations in membrane proteins result in human diseases. Although integral membrane proteins provide daunting technical challenges for all methods of protein structure determination, nuclear magnetic resonance (NMR) spectroscopy can be an extremely versatile and powerful method for determining their structures and characterizing their dynamics, in lipid environments that closely mimic the cell membranes. Once milligram amounts of isotopically labeled protein are expressed and purified, micelle samples can be prepared for solution NMR analysis, and lipid bilayer samples can be prepared for solid-state NMR analysis. The two approaches are complementary and can provide detailed structural and dynamic information. This paper describes the steps for membrane protein structure determination using solution and solid-state NMR. The methods for protein expression and purification, sample preparation and NMR experiments are described and illustrated with examples from the FXYD proteins, a family of regulatory subunits of the Na,K-ATPase.

Nuclear magnetic resonance structural studies of membrane proteins in micelles and bilayers

Nuclear magnetic resonance (NMR) spectroscopy enables determination of membrane protein structures in lipid environments, such as micelles and bilayers. This chapter outlines the steps for membrane-protein structure determination using solution NMR with micelle samples, and solid-state NMR with oriented lipid-bilayer samples. The methods for protein expression and purification, sample preparation, and NMR experiments are described and illustrated with examples from gamma and CHIF, two membrane proteins that function as regulatory subunits of the Na+- and K+-ATPase.

Correlation of gene and protein structures in the FXYD family proteins

The FXYD family proteins are auxiliary subunits of the Na,K-ATPase, expressed primarily in tissues that specialize in fluid or solute transport, or that are electrically excitable. These proteins range in size from about 60 to 160 amino acid residues, and share a core homology of 35 amino acid residues in and around a single transmembrane segment. Despite their relatively small sizes, they are all encoded by genes with six to nine small exons. We show that the helical secondary structures of three FXYD family members, FXYD1, FXYD3, and FXYD4, determined in micelles by NMR spectroscopy, reflect the structures of their corresponding genes. The coincidence of helical regions, and connecting segments, with the positions of intron-exon junctions in the genes, support the hypothesis that the FXYD proteins may have been assembled from discrete structural modules through exon shuffling.

Protonation-dependent inactivation of Na,K-ATPase by hydrostatic pressure developed at high-speed centrifugation

Irreversible inactivation of membranous Na,K-ATPase by high-speed centrifugation in dilute aqueous solutions depends markedly on the protonation state of the protein. Pig kidney Na,K-ATPase is irreversibly inactivated at pH 5 but is fully protected at pH 7 and above. Shark rectal gland Na,K-ATPase is irreversibly inactivated at neutral or acidic pH and partially protected at an alkaline pH. The overall Na,K-ATPase activity and the K-dependent pNPPase activity were denatured in parallel. Cryoprotectants such as glycerol or sucrose at concentrations of 25-30% fully protect both enzymes against inactivation. The specific ligands NaCl and KCl protect the Na,K-ATPase activity partially and the pNPPase activity fully at concentrations of 0.2-0.3 M. Electron microscope analysis of the centrifuged Na,K-ATPase membranes revealed that the ultrastructure of the native membranes is preserved upon inactivation. It was also observed that the sarcoplasmic reticulum Ca-ATPase and hog gastric H, K-ATPase are susceptible to inactivation by high-speed centrifugation in a pH-dependent fashion. H,K-ATPase is protected at alkaline pH, whereas Ca-ATPase is protected only in the neutral pH range.

Electric parameters of Na+/K(+)-ATPase by measurements of the fluorescence-detected electric dichroism

The electric parameters of Na+/K(+)-ATPase labeled by FITC have been characterized by measurements of the fluorescence-detected electric dichroism. The fluorescence emission was measured with polarizers at the magic angle and the light for excitation was usually polarized parallel to the field vector. The FITC-Na+/K(+)-ATPase preparations exhibit a negative electric dichroism at field strengths up to about 600 V/cm and a positive dichroism at higher field strengths. Pulse reversal experiments reveal a dominant permanent electric moment at low electric field strengths and an increasing contribution from an induced electric moment at higher field strengths. The dichroism rise curves and the transients upon pulse reversal show two relaxation processes with opposite amplitudes, whereas the dichroism decay curves in most cases can be represented by single exponentials at a reasonable accuracy. The amplitude A2 associated with the slower of the rise processes is dominant at low field strengths and also approaches saturation already at low field strengths. The dependence of A2 on the electric field strength is consistent with the orientation function for permanent dipoles and cannot be represented by the orientation function for induced dipoles. The fitted permanent dipole moment is in the range of 3.5 x 10(-24) Cm [1 x 10(6) D] and shows only a relatively small decrease with increasing ionic strength. The stationary values of the electric dichroism up to field strengths E < or = 800 V/cm can be represented with high accuracy by an orientation function for disk-shaped particles with a permanent moment along the particle symmetry axis and an induced moment along the semi-major axis. The permanent electric moment determined according to this function is consistent with the one obtained from the amplitudes A2. In summary, our measurements indicate that Na+/K(+)-ATPase is associated with a large permanent electric moment directed perpendicular to the membrane plane. The dipole moment per ATPase monomer unit is estimated to be 1.4 x 10(-27) Cm [430 +/- 50 D].

Ultrastructure of membrane-bound Na, K-ATPase after extensive tryptic digestion

Membrane-bound Na, K-ATPase was digested with trypsin in the presence of Rb+ to form the stable 19-kDa and smaller fragments of the alpha-chain known to preserve occlusion of Rb+ (K+) or Na+. The trypsinized membranes obtained from pig kidney and shark rectal gland were analyzed by electron microscopy. Tryptic digestion preserved general membrane structure but removed both the surface particles observed by negative staining and the protruding cytoplasmic portion of the alpha-subunit identified in thin sections. However, intramembrane particles defined by freeze-fracture were preserved after trypsinization suggesting that the remaining membrane spanning protein fragments retain the native structure within the lipid bilayer after proteolysis.

Reconstitution of Na+/K+-ATPase into phosphatidylcholine vesicles by dialysis of nonionic alkyl maltoside detergents

The reconstitution of Na+/K+-ATPase from outer medulla of rabbit kidney into large unilamellar liposomes was achieved through detergent removal by dialysis of mixed micellar solutions of synthetic dioleoyl phosphatidylcholine/octyl glucoside and Na+/K+-ATPase/decyl maltoside or decenyl maltoside. Tight, transport-active liposomes were formed when the lipid and the enzyme were solubilized separately in the nonionic detergents and mixed immediately before starting the dialysis. The two maltoside detergents with different structures of the hydrophobic part of the molecule proved to be well suited for the solubilization of Na+/K+-ATPase with high retention of enzyme activity; the inactivation of enzyme being evidently slower with the unsaturated decenyl maltoside. The diameters of the proteoliposomes, 110 and 170 nm, respectively, were also dependent on the structure of the maltoside detergent, the saturated decyl maltoside producing the bigger liposomes. After freeze-fracture, both preparations exhibited intramembranous particles as structural indicators of successful reconstitution. The electrogenic activity of the reconstituted enzyme was determined by fluorescence measurements with Oxonol VI and by tracer-flux measurements with 22Na+.