Protein bridge

EejSiJ cluster of Fe-protein, bridges between Fe- and MoFeproteins... 

Chemical and spectral studies have indicated that in addition to bridging exogenous ligands, there is an endogenous protein bridge at the coupled binuclear copper site. Evidence for this is seen with the half-met derivative and the binuclear cupric derivatives met and dimer. 

Fig. 42. Spectroscopically effective active site representations of the coupled binuclear copper site (left) and the type 3 site in Rhus laccase (right) where OR and R represent endogenous protein bridges in the respective sites...

Where protein structures are well established, the match with model complexes is good both structurally and spectroscopically, although the protein bridging units are less symmetrical (175). This agreement then provies a basis for predicting structures based on partial data, such as metal-metal distances from EXAFS or characteristic electronic spectra. Model systems for the Fe—0—Fe proteins have been comprehensively reviewed (173-175) and only the macrocyclic systems will be considered here. 

Mueller-Storm HP, Sogo JM, Schaffner W. 1989. An enhancer stimulates transcription in trans when attached to the promoter via a protein bridge. Cell 58, 767-717. 

A FIGURE 19-5 Actin cross-linking proteins bridging pairs of actin filaments, (a) When cross-linked by fimbrin (red), a short protein, actin filaments pack side by side to form a bundle. 

Pathways Versus Tubes. The essential idea from the pathway approximation is that the Hamiltonian is converted to a searchable network, and one can compute estimates of Tda that are (1) simple products corresponding to the number of bonds involved, and (2) expected to be correct (up to a prefactor) if the couphng provided by the entire protein bridge is well approximated by only the states included on the pathway tube. The concept of finding a best path is dependent on this concept of defining the coupling as a product of constant factors. 

Surface Force Measurements. This technique enables the measurement of the force (10 mN accuracy) versus distance (0.1-0.2 nm accuracy) between two curved mica surfaces. The forces between two solid surfaces across an aqueous solution are highly sensitive to the structure of the solid/liquid interfaces. When such surfaces are covered with adsorbed protein layers, then, the analysis of the force/distance profiles may reveal the formation of protein bridges between the two surfaces, the occurrence of steric interactions, or any possible protein conformation change. 

In the case of diluted suspensions (CsiO2=0.1-0.2 wt%), the adsorption ino-eases up to 1.5-4.5 g/g due to intensive flocculation of proteins with silica aggregates by formation of protein bridges between them. The adsorption of proteins increases with increasing 5bct and Cqh values (Figure 1.178). 

In the present work, three aggregation mechanisms have been considered to explain the experimental results at short aggregation times (1) coagulation, where bonds are formed between two uncovered surface patches of the colliding particles (2) weak flocculation, that is, two covered patches and (3) pure bridging flocculation, where the collision of an uncovered part of one particle with the covered part of another particle occurs. In this configuration, a protein bridge will form between the particles. 

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