Prosthetic group structural protein

Structure of the MoFe Protein. Extensive spectroscopic studies of the MoEe proteia, the appHcation of cluster extmsion techniques (84,151), x-ray anomalous scattering, and x-ray diffraction (10,135—137,152) have shown that the MoEe proteia contains two types of prosthetic groups, ie, protein-bound metal clusters, each of which contains about 50% of the Ee and content. Sixteen of the 30 Ee atoms and 14—16 of the 32—34... 

These are rarely found free but occur as a common prosthetic group of proteins. The first such protein to be extensively studied was the iron porphyrin (Greek porphyra, purple) haemoglobin. This and other iron-porphyrin proteins play a vital role in the physiological activity of nearly all forms of life.146 These forms have the same basic structure (39) but differ in the nature of the pyrrole substituents these are shown for the major porphyrins in Table 13. It has become common practice to refer to all the iron-porphyrin proteins as haem proteins. The function of haemoglobin is, of... 

Figure 28. Plausible structure of reconstituted Mb-cytocyhrome c complex. Green protein is the reconstituted Mb. Blue molecule represents the artificially created hemin as a prosthetic group. Pink protein is cytochrome c and red molecule is heme c in cytochrome c. The structure was generated by computer simulation.

In spite of the close theoretical relationship between EPR and NMR spectroscopy, EPR has only very narrow applications. The primary reason for this is that the EPR phenomenon is spectroscopically silent unless there are unpaired electrons. Most biological macromolecules are closed shell molecules and contain no unpaired electrons. Therefore, EPR is of little real value for biological macromolecular structure characterisation. The only exception to this rule is that certain prosthetic groups in proteins may contain redox active metal centres/clusters that have transient or even permanent unpaired electrons (see Chapter 4). These metal centres/ clusters can be studied by EPR spectroscopy in order to demonstrate the presence of unpaired electrons. Thereafter, EPR data may then be used to derive the relative structural arrangements of metals within centres or clusters, and to assign putative distributions of redox states should there be any obvious redox heterogeneity. EPR is also useful to detect transient or even metastable radical formation during bio catalysis (see Chapter 8). 

The presence of a cofactor or a prosthetic group in protein structure, by helping the folding process and stabilizing the structure, represents a particular case (this point is discussed in detail in Chapter 11). 

Koda, P., and Lee, J. (1979). Separation and structure of the prosthetic group of the blue fluorescence protein from the bioluminescent bacterium Photobacterium phosphoreum. Proc. Natl. Acad. Sci. USA 76 3068-3072. 

Glucose oxidase (GOD) is a typical flavin enzyme with flavin adenine dinucleotide (FAD) as redox prosthetic group. Its biological function is to catalyze glucose to form gluconolaction, while the enzyme itself is turned from GOD(FAD) to GOD(FADH2). GOD was used to prepare biosensors in extensive fields. Many materials that can be used to immobilize other proteins can be suitable for GOD. GOD adsorbed on CdS nanoparticles maintained its bioactivity and structure, and could electrocatalyze... 

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. 

Electron transfer (ET) is a key reaction in biological processes such as photosynthesis and respiration [1], Photosynthetic and respiratory chain redox proteins contain one or more redox-active prosthetic groups, which may be metal complexes or organic species. Since it is known from crystal structure analyses that the prosthetic groups often are located in the protein interior, it is likely that ET in protein-protein complexes will occur over large molecular distances ( > 10 A) [2-4],... 

Fig. 1. Space filling model of yeast iso-1-cytochrome c. The edge of the heme prosthetic group is visible as a black linear structure in the center of the protein. Phe-82 is shaded a dark gray at the left upper side of the heme group...

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