Interface recognition site

Recently an X-ray structure became available for the bovine enzyme (24). This, combined with the results from numerous studies on this enzyme by De Haas and his coworkers has led to a mechanistic model for the catalytic activity. Another problem is the mode of activation of the pro-enzyme and the nature of the interface recognition site. The photo-CIDNP method has shed some light on this latter problem. 

Summarizing the CIDNP results (see also Table I) it appears that Trp 3 and Trp 69 (and Tyr 19 in the equine enzyme but not Tyr 123 in the porcine enzyme) are part of the interface recognition site of pancreatic phospholipases A. These residues are equally accessible in the pro-enzymes, out apparently a change in conformation of the N-terminal region is necessary to establish the micelle binding properties. 

Like the protein and inositide kinases, the 3D structures of APHs display two distinct domains The N-terminal P-sheet region is responsible for ATP binding, and the a-helical C-terminal provides the aminoglycoside recognition site. The active site, where phosphate transfer occurs, lies at the interface of the two domains. APHs also contain the H-G/N-D-XXXX-N sequence motif, which is common among protein kinases and involved in phosphate transfer catalysis. Structural homology to protein kinases is extended to function, as it has been demonstrated that APHs have weak but measurable protein kinase activity. ... 

Various Designs of Molecular Recognition Sites at Interfaces... 

In general terms, the crystallographic results show that lipases contain several distinct sites, each responsible for a specific function. The hydrolysis of the ester bond is accomplished by the catalytic triad, responsible for nucleophilic attack on the carbonyl carbon of the scissile ester bond, assisted by the oxyanion hole, which stabilizes the tetrahedral intermediates. The fatty acid recognition pocket defines the specificity of the leaving acid. There is also one or more interface activation sites, responsible for the conformational change in the enzyme. In this section the discussion is on the available structural data relevant to the function of all these sites. 

The lids constitute the interface recognition and activation sites. Their topology with respect to the active sites in the three known structures of lipases is shown in Fig. 8. 

The crystal structures of lipases described to date are static descriptions of conformational states, possibly stabilized in some cases by crystal packing interactions. What is lacking is the dynamic component What initiates the conformational transition Is there a true lipid-recognition site that triggers the change, and does a simple two-state model come sufficiently close to the actual phenomenon Or, does the interface simply stabilize one of the conformations existing in solution in an equilibrium And just how stable is the inactive conformation ... 

Pieterson, W. A., Vidal, J. C., Volwerk, J.J., and de Haas, G. H. (1974b). Zymogen-catalyzed hydrolysis of monomeric substrates and the presence of a recognition site for lipid-water interfaces to phospholipase As. Biochemistry IS, 1455—1460. 

Lahav, M. Katz, E. Willner, I., Photochemical imprint of molecular recognition sites in two-dimensional monolayers assembled on au electrodes Effects of the monolayer structures on the binding affinities and association kinetics to the imprinted interfaces, Langmuir 2001,17, 7387-7395... 

Polyamino acids can be considered as models for conformational studies, providing an atomistic description of the secondary structural motifs typically found in proteins [30-39]. Two-dimensional hydrogen-bonded layers and columns in the structures of crystalline amino acids can mimic S-sheets and helices in proteins and amyloids [40 5], and can be compared with two-dimensional crystalline layers at interfaces [46-58]. Nano-porous structures of small peptides can mimic cavities in proteins [24, 59-63]. One can also prepare crystals in which selected functional groups and side chains are located with respect to each other in the same way, as at recognition sites of substrate-receptor complexes, and use the systems to simulate the mutual adaptation of components of the complex responsible for recognition. 

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