Proteins and Their Structures

Muscle Proteins and Their Structures 1120 Box 19-C Actin-Based Motility and Bacterial... 

There is a severe practical problem in looking for correlations between the rate constants for folding of small proteins and their structural or thermodynamic properties—specific structural features can dominate the rate of folding. For example, we know from the protein engineering studies on barnase and CI2 that specific mutations can slow down the rate of folding by several orders of... 

Mononuclear Fe centers in an approximately tetrahedral environment of cysteinyl-S (Rd-type centers) (see Figure 1) mediate electron transfer in a variety of different bacterial proteins and their structures and properties have recently... 

A cell contains a myriad of proteins. The individual proteins are separated and identified to understand the nature of different proteins and their structural and functional relationships. Proteins are isolated by a variety of means because they have a diverse set of properties. A multidimensional approach is more suitable to separate them than a single approach, as outlined in Chapter 1. Such a multidimensional approach must address the problems concerning their resolution, high throughput, automation, and adaptability to analysis by mass spectrometry. One of the most important ways they are separated is by electrophoresis, including the two-dimensional (2D) gel electrophoresis and capillary electrophoresis. After their separation by these methods, they are identified by use of a mass spectrometry. These methods are described in this chapter. 

More difficult, but also proniising to be honoured with success proves the isolation of pure, integral membrane proteins and their structure analysis by diffraction techniques. One avenue is given by defined solubilization with detergents and the evaluation of the small-angle (particle) scattering pattern from dilute solution (for reviews on this method, see Refs. and ). This has so far been attempted with bovine rhodopsin, the major protein component of retinal rod outer sement membranes with the Ca -dependent ATPase from sarcoplasmic reticulum... 

Occurrence of Oligomeric Proteins and Their Structural Characteristics... 

Even though dynein, kinesin, and myosin serve similar ATPase-dependent chemomechanical functions and have structural similarities, they do not appear to be related to each other in molecular terms. Their similarity lies in the overall shape of the molecule, which is composed of a pair of globular heads that bind microtubules and a fan-shaped tail piece (not present in myosin) that is suspected to carry the attachment site for membranous vesicles and other cytoplasmic components transported by MT. The cytoplasmic and axonemal dyneins are similar in structure (Hirokawa et al., 1989 Holzbaur and Vallee, 1994). Current studies on mutant phenotypes are likely to lead to a better understanding of the cellular roles of molecular motor proteins and their mechanisms of action (Endow and Titus, 1992). 

The six major proteins of milk, asl-, o s2-, and /c-casein, jS-lactoglobulin, and a-lactalbumin, contain at least one tryptophan residue [57], the fluorescence of which allows the monitoring of the structural modifications of proteins and their physicochemical environment during the coagulation processes. Emission fluorescence spectra of the protein tryptophanyl residues were recorded for the milk coagulation kinetics induced by... 

It is quite evident that the ferrous complexes of porphyrins, both natural and synthetic, have extremely high affinities towards NO. A series of iron (II) porphyrin nitrosyls have been synthesized and their structural data [11, 27] revealed non-axial symmetry and the bent form of the Fe-N=0 moiety [112-116]. It has been found that the structure of the Fe-N-O unit in model porphyrin complexes is different from those observed in heme proteins [117]. The heme prosthetic group is chemically very similar, hence the conformational diversity was thought to arise from the steric and electronic interaction of NO with the protein residue. In order to resolve this issue femtosecond infrared polarization spectroscopy was used [118]. The results also provided evidence for the first time that a significant fraction (35%) of NO recombines with the heme-Fe(II) within the first 5 ps after the photolysis, making myoglobin an efficient N O scavenger. 

These organelles occur in the endosperm of cereal grains and their structures are tissue specific. They are about 2-5 im in diameter and often contain globoid and occasionally crystalloid inclusions. Prolamin accumulates in small or large spherical bodies. Crystalline protein bodies are the sites of accumulation of nonprolamin storage proteins. 

Figure 6.2. Structure of heterotrimeric G-proteins. The generalised structure of the a-, /3-, and y-subunits of the heterotrimeric G-proteins and their organisation in the plasma membrane are shown.

The dynamics of protein molecules have been studied intensively using various experimental19-U) and theoretical112 approaches. Luminescence methods are widely applied in these investigations.12 18) Modem concepts about the structure of proteins and their dynamics which have evolved from these investigations are presented briefly in this section. 

The real value in the genome sequence is to find out the regions of the genome that encode proteins. Proteomics, the study of the structures and functions of proteins, further enhances our understanding of proteins and their functions, leading to insights on how they are affected in normal and disease conditions. Exhibit A2.3 shows some of the medical conditions due to genetic problems. 

The basic problem with the lock and key analogy is that locks and keys are generally rigid structures while proteins and their substrates have substantial freedom of movement that is, proteins and their substrates have a number of conformations available to them in space and they change conformation a few billion times per second. So, our biological locks and keys are wobbly. 

Every cell possesses a plasma (or cell) membrane which isolates its contents from its surroundings. This membrane consists of a double layer of phospholipid molecules with proteins attached or dispersed within. The uneven distribution of proteins and their ability to move in the plane of the membrane led to the description of this structure as a fluid mosaic (Figure 1.2) (Chapter 5). Some of these proteins facilitate the transport of molecules and ions through the membrane, while others are receptors for extracellular molecules which provide information about conditions in adjacent cells, blood and elsewhere in the body. Physical or chemical damage to these membranes can render them leaky so that, for example, Na and Ca ions, the concentrations of which are much higher in the extracellular fluid, can enter the cell causing damage. On the outer surface of... 

---