Acyl lipids in Arabidopsis and all other plants have a myriad of diverse functions. These include providing the core diffusion barrier of the membranes that separates cells and subcellular organelles. This function alone involves more than 10 membrane lipid classes, including the phospholipids, galactolipids, and sphingolipids, and within each class the variations in acyl chain composition expand the number of structures to several hundred possible molecular species. Acyl lipids in the form of triacylglycerol account for 35% of the weight of Arabidopsis seeds and represent their major form of carbon and energy storage. A layer of cutin and cuticular waxes that restricts the loss of water and provides protection from invasions by pathogens and other stresses covers the entire aerial surface of Arabidopsis. Similar functions are provided by suberin and its associated waxes that are localized in roots, seed coats, and abscission zones and are produced in response to wounding. This chapter focuses on the metabolic pathways that are associated with the biosynthesis and degradation of the acyl lipids mentioned above. These pathways, enzymes, and genes are also presented in detail in an associated website (ARALIP: http://aralip.plantbiology.msu.edu/). Protocols and methods used for analysis of Arabidopsis lipids are provided. Finally, a detailed summary of the composition of Arabidopsis lipids is provided in three figures and 15 tables.

/pdf/acyl-lipid-metabolism-2156uh7qdu.pdf

Acyl-Lipid Metabolism

Dielectric Relaxation and Solvation Dynamics of Water in Complex Chemical and Biological Systems

This article, on protein-based polymers comprised of repeating peptide sequences, reviews studies from the author's laboratory covering a period of more than two decades; it presents a general mechanism for protein folding and function and demonstrates the mechanism by designing model proteins capable of performing many of the energy conversions that sustain life and by designing diverse biomolecular machines and materials with promising applications for society. All polymers with the correct balance of apolar and polar moieties, including water soluble proteins and protein-based polymers, increase order by a hydrophobic folding and assembly transition as the temperature is raised above a critical onset temperature, designated as Tt. Instead of varying the temperature, however, innumerable variables lower the value of Tt from above to below the operating temperature to drive folding and function. Thus, this inverse temperature transition provides a fundamental mechanism whereby proteins fold and function ...

Physical Chemistry of Biological Free Energy Transduction As Demonstrated by Elastic Protein-Based Polymers†

Surface vibrational spectroscopy by sum-frequency generation was used to study hydrophobicity at the molecular level at various interfaces: water-surfactant-coated quartz, water-hexane, and water-air. In all cases, hydrophobicity was characterized by the appearance of dangling hydroxyl bonds on 25 percent of the surface water molecules. At the water-quartz interface, packing restrictions force the water surface layer to have a more ordered, ice-like structure. A partly wettable water-quartz interface was also studied.

https://science.sciencemag.org/content/sci/264/5160/826.full.pdf

Surface Vibrational Spectroscopic Studies of Hydrogen Bonding and Hydrophobicity

The properties of water in biological systems have been studied for well over a century by a wide range of physical techniques, but progress has been slow and erratic. Protein hydration--the perturbation of water structure and dynamics by the protein surface--has been a particularly rich source of controversy and confusion. Our aim here is to critically examine central concepts in the description of protein hydration, and to assess the experimental basis for the current view of protein hydration, with the focus on dynamic aspects. Recent oxygen-17 magnetic relaxation dispersion (MRD) experiments have shown that the vast majority of water molecules in the protein hydration layer suffer a mere twofold dynamic retardation compared with bulk water. The high mobility of hydration water ensures that all thermally activated processes at the protein-water interface, such as binding, recognition and catalysis, can proceed at high rates. The MRD-derived picture of a highly mobile hydration layer is consistent with recent molecular dynamics simulations, but is incompatible with results deduced from intermolecular nuclear Overhauser effect spectroscopy, dielectric relaxation and fluorescence spectroscopy. It is also inconsistent with the common view of hydration effects on protein hydrodynamics. Here, we show how these discrepancies can be resolved.

/pdf/protein-hydration-dynamics-in-solution-a-critical-survey-543043s61t.pdf

Protein hydration dynamics in solution: a critical survey

In one of the earliest reports of the physicochemical properties of a protein, Sorensen (1) asked "Does crystallised egg-albumin contain water?" Fol­ lowing a detailed compositional analysis, he found that such samples contain about 0.22 g water per g water-free egg-albumin. In later work, he gives the water content of crystallized hemoglobin as 0.35 gjg (2). We now know that protein molecules can have from 0.20 to 0.70 g strongly associated (bound) water per g protein, and through modern x-ray and neutron diffraction studies, we have for some proteins a detailed knowledge of the location and bonding of much of this water (3-5). By using the latest high-resolution NMR techniques, we can even identify individual molecules of hydration water and characterize their binding sites on the protein molecule (6). Thus, in general and as a convenient method of classification, two kinds of water molecules associated with proteins have been identified: internal water and peripheral water. The internal water molecules, which form an integral part of a protein structure, diminish local charge-charge inter­ actions and reduce destabilizing effects that arise from otherwise unbonded proton donors and acceptors (7, 8). These molecules exchange with bulk water in time scales ranging from tens of seconds to months (9, 1 0). As a rough gauge of the upper limit of internal water, we can consider the small

R Pethig

Papers

Protein-water interactions determined by dielectric methods.