Protein behavior

Many complex systems have been spread on liquid interfaces for a variety of reasons. We begin this chapter with a discussion of the behavior of synthetic polymers at the liquid-air interface. Most of these systems are linear macromolecules however, rigid-rod polymers and more complex structures are of interest for potential optoelectronic applications. Biological macromolecules are spread at the liquid-vapor interface to fabricate sensors and other biomedical devices. In addition, the study of proteins at the air-water interface yields important information on enzymatic recognition, and membrane protein behavior. We touch on other biological systems, namely, phospholipids and cholesterol monolayers. These systems are so widely and routinely studied these days that they were also mentioned in some detail in Chapter IV. The closely related matter of bilayers and vesicles is also briefly addressed. 

Swedberg, S. A., Characterization of protein behavior in high-performance capillary electrophoresis using a novel capillary system, Anal. Biochem., 185, 51, 1990. 

The capability to analyze 2DLC data by the automated process, and the ability to resolve component-level behaviors within complex protein separations enabled us to undertake a subsequent series of comparative experiments where protein behaviors within a cellular lysate were analyzed using both step and linear gradients in a 2DLC/MS experiment. This will be described in the following sections of this chapter. 

To illustrate these methods, we consider the main biological problems that have motivated their development. The problems that have received the most attention are the receptor-ligand binding problem [12-16] and the calculation of proton binding affinities (pKa shifts) [17-20], The methods described can also be applied to many related problems, such as redox protein behavior, protein-protein association, protein folding, or membrane insertion. 

Although protein behavior in SDS-containing buffers is qualitatively different from small molecules, applications of MEKC-type conditions have been applied to many protein separations. In applications using uncoated capillaries, protein-wall interactions are eliminated because of the anionic character of SDS-protein complexes. In applications using coated capillaries with no EOF, the high electrophoretic mobility of SDS-protein complexes can decrease analysis time. 

The main goal of the proteomic research is to find the distinction between quantitative regulation and structural proteomics. Today, the core technology of proteomics is 2DE (two-dimensional electrophoresis) coupled with MS (mass spectrometry). It offers the most widely accepted way of gathering qualitative and quantitative protein behavioral data in cells, tissues, and fluids to form proteomic databases. 

The failure of the theory indicates that soy protein behavior is more complex than Melander and Horvath s (7, ) model. In deriving their simple theory, Melander and Horvath assumed that the changes in hydrophobic surface area, in the dipole moment, and in the net charge of the protein upon solubilization are invariant with respect to salt species or salt concentration. In other words, they assumed that the soluble proteins have the same thermodynamic state regardless of salt species or salt concentration. The results for soy proteins can be treated in the framework of the Melander and Horvath s theory if it is expanded to allow the exposed surface area, the dipole moment, and the net protein charge to be functions of the salt species and the salt concentration. 

Thus, there are three different ways to account for this soy protein behavior as follows ... 

The topic of this chapter deals witK the effect of proteolytic enzyme action on functionality. As noted by Whitaker ( ), protein functionality can be altered by many different types of enzymes. However, since the great majority of enzymes which modify protein behavior in food systems are proteases, we will confine our discussion to them. 

It is known that the method used to truncate the interatomic interactions can have an important effect. It has been demonstrated that the dielectric properties of simulated water are a sensitive function of the extent to which the long-range electrostatic interactions are included [40]. Simulations of phospholipid membrane-water systems showed that the behavior of the water near the membrane is incorrectly described if the electrostatic interactions are truncated at too short a distance, and hot water/cold-protein behavior is observed [10]. Given the importance of the potential/force truncation, we have investigated this issue for the copper system being simulated. This has been done in terms of the same properties as were used in examining convergence. 

The knowledge of the Kirkwood-Buff integrals for dilute mixtures can be very helpful in the analysis of the local water/cosolvent composition in the vicinity of a solute molecule. Ultimately, it can provide information about the effect of various cosolvents on the protein behavior in aqueous solutions. 

Many characteristics of a protein in aqueous solvents are connected to its preferential solvation (or preferential hydration). The protein stability is a well-known example. Indeed, the addition of certain compounds (such as urea) can cause protein denaturation, whereas the addition of other cosolvents, such as glycerol, sucrose, etc. can stahihze at high concentrations the protein stiucture and preserve its en2ymatic activity [4-7]. The analysis of literature data shows that as a rule Ffor the former and r23 " <0 for the latter compounds. Recently, the authors of the present paper showed how the excess (or deficit) number of water (or cosolvent) molecules in the vicinity of a protein molecule can be calculated in terms of F2 the molar volume of the protein at infinite dilution and the properties of the protein-free mixed solvent [8]. The protein solubility in an aqueous mixed solvent is another important quantity which can be connected to the preferential solvation (or hydration) [9-13] and can help to understand the protein behavior [9-17]. 

Day, R.N. (2005) Imaging protein behavior inside the living cell. Mol. Cell. Endocrinol., 230, 1-6. 

Fluorescent spectroscopy, because of its high level of sensitivity, has long been a powerful method for studying protein behavior. Site-specific attachment of fluorophores to a unique cysteine in a protein of interest is a traditional route for the production of fluorescent proteins. In addition, the discovery of fluorescent proteins, such as the green fluorescent protein (GFP) from the jellyfish Aequorea victoria [62], has provided a genetic approach for the production of fluorescently labeled proteins. Both these methods, however,... 

It is likely that experimentally found values of molecular cross-sectional areas do not correspond to the equilibrium states of the protein layers but reflect only the transition state configuration, as assumed by MacRitchie [16] and depicted in Fig. 1. The problem of adsorption reversibility is basic for understanding the protein behavior at interfaces. The belief in the protein adsorption irreversibility is mainly based on drastic conformational changes in interfacial film and the great difficulty of desorbing a protein from this film [15], However, these criteria are not always a proof of irreversibility. It was shown in many cases [3,24,39-41] that proteins can be desorbed... 

---