Welcome to the Club?: A response to The Cross -Border Connection by Roger Waldinger

Roger Waldinger's provocative book on migrants’ cross-border lives corroborates many insights already established by transnational migration scholarship. He makes a compelling case for the need to understand migration not just as assimilation – neo, segmented, or otherwise – but also as about how people continue to be simultaneously involved in their homelands, the countries where they settle, and other salient places. I am glad that Waldinger has lent his voice to correct the unproductive divide between immigration and emigration scholarship. But the ‘new’ path he charts forward to right what he sees as wrong with current scholarship is, at times, so selectively formulated and argued that it undercuts its effectiveness.     

Interrelations between photoperiod, frost hardiness and sulfhydryl groups in cabbage

Hardening of SD (8 and 12 hrs) and LD (18- and 24-hr photoperiods) cabbage plants in stages at temperatures starting with + 5° and ending with − 3° led to the following changes:

Soluble protein plus nonprotein N showed a net increase only in the SD plants. In both SD and LD plants, it decreased to a minimum toward the end of the first stage of hardening, increased to a maximum in the second stage. The degree of this change was proportional to the photoperiod. These changes were mainly due to the proteins.

As in previous investigations, SH content rose during the first 1 to 2 weeks, but only in the SD plants. This rise was primarily due to the protein fraction. After the first 1 to 2 weeks both SD and LD plants showed a decrease in SH content, most pronouncedly during the second stage of hardening.

Nonprotein SH content was very low and decreased during hardening in both SD and LD plants. Nonprotein SS increased during the first stage of hardening. Total nonprotein SH+2SS rose to a maximum during the first stage of hardening, paralleling both osmotic potential and hardiness. During the second stage the total decreased, in spite of the rise in hardiness. These results held true for both SD and LD plants.

These results are all explainable on the basis of the SHSS theory of frost resistance.

     

Accuracy of side-chain prediction upon near-native protein backbones generated by ab initio folding methods

The ab initio folding problem can be divided into two sequential tasks of approximately equal computational complexity: the generation of native-like backbone folds and the positioning of side chains upon these backbones. The prediction of side-chain conformation in this context is challenging, because at best only the near-native global fold of the protein is known. To test the effect of displacements in the protein backbones on side-chain prediction for folds generated ab initio, sets of near-native backbones (≤ 4 Å Cα RMS error) for four small proteins were generated by two methods. The steric environment surrounding each residue was probed by placing the side chains in the native conformation on each of these decoys, followed by torsion-space optimization to remove steric clashes on a rigid backbone. We observe that on average 40% of the χ1 angles were displaced by 40° or more, effectively setting the limits in accuracy for side-chain modeling under these conditions. Three different algorithms were subsequently used for prediction of side-chain conformation. The average prediction accuracy for the three methods was remarkably similar: 49% to 51% of the χ1 angles were predicted correctly overall (33% to 36% of the χ1+2 angles). Interestingly, when the inter-side-chain interactions were disregarded, the mean accuracy increased. A consensus approach is described, in which side-chain conformations are defined based on the most frequently predicted χ angles for a given method upon each set of near-native backbones. We find that consensus modeling, which de facto includes backbone flexibility, improves side-chain prediction: χ1 accuracy improved to 51–54% (36–42% of χ1+2). Implications of a consensus method for ab initio protein structure prediction are discussed. Proteins 33:204–217, 1998. © 1998 Wiley-Liss, Inc.     

Towards an interpretation of 13C chemical shifts in bathorhodopsin,a functional intermediate of a G-protein coupled receptor

Photoisomerization of the membrane-bound light receptor protein rhodopsin leads to an energy-rich photostate called bathorhodopsin, which may be trapped at temperatures of 120 K or lower. We recently studied bathorhodopsin by low-temperature solid-state NMR, using in situ illumination of the sample in a purpose-built NMR probe. In this way we acquired ¹³C chemical shifts along the retinylidene chain of the chromophore. Here we compare these results with the chemical shifts of the dark state chromophore in rhodopsin, as well as with the chemical shifts of retinylidene model compounds in solution. An earlier solid-state NMR study of bathorhodopsin found only small changes in the ¹³C chemical shifts upon isomerization, suggesting only minor perturbations of the electronic structure in the isomerized retinylidene chain. This is at variance with our recent measurements which show much larger perturbations of the ¹³C chemical shifts. Here we present a tentative interpretation of our NMR results involving an increased charge delocalization inside the polyene chain of the bathorhodopsin chromophore. Our results suggest that the bathochromic shift of bathorhodopsin is due to modified electrostatic interactions between the chromophore and the binding pocket, whereas both electrostatic interactions and torsional strain are involved in the energy storage mechanism of bathorhodopsin.     

Steady-State Acceptor Fluorescence Anisotropy Imaging under Evanescent Excitation for Visualisation of FRET at the Plasma Membrane

We present a novel imaging system combining total internal reflection fluorescence (TIRF) microscopy with measurement of steady-state acceptor fluorescence anisotropy in order to perform live cell Förster Resonance Energy Transfer (FRET) imaging at the plasma membrane. We compare directly the imaging performance of fluorescence anisotropy resolved TIRF with epifluorescence illumination. The use of high numerical aperture objective for TIRF required correction for induced depolarization factors. This arrangement enabled visualisation of conformational changes of a Raichu-Cdc42 FRET biosensor by measurement of intramolecular FRET between eGFP and mRFP1. Higher activity of the probe was found at the cell plasma membrane compared to intracellularly. Imaging fluorescence anisotropy in TIRF allowed clear differentiation of the Raichu-Cdc42 biosensor from negative control mutants. Finally, inhibition of Cdc42 was imaged dynamically in live cells, where we show temporal changes of the activity of the Raichu-Cdc42 biosensor.     

Maturational changes in steroidogenesis in the inner and outer zones of the guinea pig adrenal cortex

Studies were done to determine the effects of age on steroidogenesis in the inner (zona reticularis) and outer (zona fasciculta plus glomerulosa) zones of the guinea pig adrenal cortex. In 35-day-old animals, cortisol production by adrenal outer zone cells was approximately twice as great as that by inner zone cells. With aging, cortisol secretion by inner zone cells decreased to very low levels, but there was no detectable change in the capacity for cortisol production by the outer zone. However, the outer zone comprised a progressively decreasing fraction of the total adrenal mass in older animals. To determine the basis for the decline in cortisol production by inner zone cells with aging, the activities of several steroidogenic enzymes were determined. Microsomal 21-hydroxylase activity was greater in the inner than outer zone but was not significantly affected by age. By contrast, 17-hydroxylase activity was greater in the outer zone at all ages, and decreased with aging in the inner but not the outer zone. Mitochondrial cholesterol sidechain cleavage and 11β-hydroxylase activities were also higher in the outer than inner zone and declined in the zone only in older animals. The decrease in inner zone cholesterol sidechain cleavage activity with aging was proportionately greater than the age-dependent changes in other enzyme activities. The results indicate that the effects of aging on steroidogenesis are both zone- and enzyme-specific. The overall decline in cortisol secretion by the guinea pig adrenal cortex with aging is attributable to both a decrease in cortisol production by the cells of the zone reticularis and a disproportionate increase in the mass of the gland comprised by this zone. The decrease in cortisol secretion correlates closely with a decline in cholesterol sidechain cleavage activity in the zona reticularis, and may be causally related.