Interfacial Binding

In this treatment we consider the binding of an interfacial enzyme to a substrate interface to be accurately described by the Langmuir adsorption 

The change in interfacial enzyme coverage (9) as a function of time can be expressed as 

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Tiss, A. Carriere, F. Verger, R. (2001). Effects of gumarabic on lipase interfacial binding and activity. Analytical Biochemistry, Vol. 294, No. 1, Quly 2001) pp. 36-43, ISSN 0003-2697. 

Gelb, M.H., Cho, W. and Wilton, D.C. (1999) Interfacial binding of secreted phospholipase A2 more than electrostatics and a major role for tryptophan. Current Opinion in Structural Biology 9, 428-432. 

The new generations of experiments are aimed at linking dynamical studies of these and other processes to the function. We have already begun research in this direction. In a recent publication [9] we reported studies of the femtosecond dynamics of an RNA-protein complex and then compared the results with those obtained for in vivo (E. Coli) transcription anti-termination activities. In two other studies we measured the activity of the protein Subtilisin Carlsberg, discussed above, to a substrate, and the role of hydration in interfacial binding and function of bovine pancreatic phospholipase at a substrate site. The goal in all these studies is to relate structures to the dynamics and hopefully to key features of the (complex ) function. 

Feng, J., Wehbi, H., and Roberts, M.F., 2002, Role of tryptophan residues in interfacial binding of phosphatidylinositol-specific phospholipase C.J.Biol. Chem. 277 19867-19875. 

M.T. Rojas, R. Koniger, J.R Stoddart, A.E. Kaifer, Supported Monolayers Containing Preformed Binding Sites - Synthesis and Interfacial Binding Properties of a Thiolated /S-Cyclodextrin Derivative , J. Am. Chem. Soc., 117, 336 (1995)... 

Understanding those components that influence the interfacial binding properties in protein/protein and protein/ligand interactions is of basic importance in protein chemistry. In this report, we have defined a system that should allow the dissection of those chemical properties that influence primary interactions via an evaluation of the transition-state thermodynamic components. 

Prior to the detailed crystallographic studies of hPL a considerable amount of biochemical data relating to the activation mechanism of hPL had been accumulated. hPL is the only lipase among the lipases with known X-ray structures for which systematic structure-function relationship studies have been initiated using site-directed mutagenesis (Lowe, 1992). Substitutions were made at positions Ser-153, His-264, and Asp-177, and measurements of catalytic activity and interfacial binding were carried out. These studies showed that the catalytic site is... 

Adsorption of SPLA2S to organized lipid-water interfaces is necessary for highly efficient catalysis ( interfacial activation ). Although the terms interfacial binding and recognition have also been used to describe this process, they are somewhat misleading because adsorption is inde-... 

Scott, D. L., Mandel, A., Sigler, P. B and Honig, B. (1993b). The electrostatic basis for the interfacial binding of secretory phospholipases Aj. In preparation. 

If we accept, for interfacial systems, the fundamental validity of the notion of a functional group a structural subunit possessing intrinsic chemical characteristics largely independent of its nearest neighbors, then it is to be expected that those aspects of reactivity influenced by interfacial binding will be limited to certain classes of effects. These are conveniently subdivided into the catagories of composition, structure, and motion. 

Lipases are interphase-active enzymes with hydrophobic domains. The hydro-phobic surface (loop) on lipase is thought to enable lipophilic interfacial binding with substrate molecules that actually induces the conformational changes in lipases. The open conformation will provide substrate with access to the active site, and vice versa. In certain types of lipases, the movements of a short a-hehcal hydrophobic loop in the lipase structure cause a conformational change that exposes the active sites to the substrate. This movement also increases the nonpolarity of the surface surrounding the catalytic site [30, 32, 34, 35]. Obviously, the hydrophobic surface plays an important role in the activity of lipase as an enzyme. 

Interfacial Binding to Tributyrin Emulsion of Native and Chemically Modified... 

Lowe, M.E. (1992) The catalytic site residues and interfacial binding of human pancreatic lipase. J. Biol. Chem. 267, 17069-17073... 

Effects of gum arable on lipase interfacial binding and activity. Anal. Biochem. 294, 36-43. 

Bezzine, S., Ferrato, F., Ivanova, M.G., Lopez, V., Verger, R. and Carriere, F. (1999) Human pancreatic lipase colipase dependence and interfacial binding of lid domain mutants. Biochemistry 38, 5499-5510. 

Buckland, A.G., Wilton, D.C. Anionic phosphohpids, interfacial binding and the regulation of cell functions. Biochim. Biophys. Acta. 1483 (2000) 199-216. 

Moreover, conformational changes in the enzyme that result from interfacial binding will allow the enzyme to express optimum activity (interfacial activation). 

The nature of interfacial binding and the rate enhancements that are achieved are controversial areas. However, it is clear that both polar and non-polar interactions are involved [6] and the precise contribution of each must depend on the nature of the phospholipid interface and the interfacial binding surface of the phospholipase. A number of factors can be considered that could make a major contribution to the enhanced hydrolysis at interfaces and these relate primarily either to the substrate or to the enzyme. 

The effect of specific phospholipid molecules on overall protein conformation and hence activity may be considered as an example of allostericity. Such allosteric behavior has been discussed in terms of a second phospholipid-binding site or as discrete interactions between the head groups of phospholipids and specific residues on the interfacial binding surface of the enzyme. The emerging evidence for sPLAjS supports a model involving multiple interactions between enzyme and interfacial lipid [8]. 

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