Acylation site

The anionic subsite (Ttp 84 and Phe 330) lies between the peripheral and acylation sites, halfway down the gorge and accommodates the positively charged quaternary ammonium of the choline moiety. Ttp 84 orients the charged part of the substrate to the active centre. This subsite is involved in a cross-talk mechanism with the peripheral anionic site (PAS) [3]. 

On the other hand, Doyle et al. have developed methyl 2-oxoimidazolidine-4(carboxylate ligands, containing 2-phenylcyclopropane attached at the 1-iV-acyl site, such as the (4(5),2 (7 ),3 (7 )-HMCPIM) ligand. The resulting dirhodium complex led, for the cyclopropanation of styrene with EDA, to the corresponding cyclopropane with 68% ee and 59% yield, but with almost... 

De Ferrari GV, Mallender WD, Inestrosa NC, Rosenberry TL (2001) Thioflavin T is a fluorescent probe of the acetylcholinesterase peripheral site that reveals conformational interactions between the peripheral and acylation sites. J Biol Chem 276(26) 23282... 

The first disclosed natural product was cerulenin (15), an irreversible inhibitor of FabB. This hydrophobic epoxide locates itself in the hydro-phobic groove of the acyl site and reacts covalently with the active site cysteine [26]. However, 15 was also found to inhibit eukaryotic fatty acid synthase. 

Scheme 15. Kinetic trapping model for the enrichment of isoprenylated proteins with a free acylation site in specific membranes...

The complex structure isolated from Scleranthus uncinatus, 5,7-dihydroxy-3 -meth-oxy-4 -acetoxyflavone-8-C-p-D-xylopyranoside-2 -0-glucoside, was determined by using ID NMR ( H, C, DEPT) and 2D NMR (H-COSY, TOCSY, HMQC, HMBC, NOESY) data sequence and linkage of the sugar chain and acylation site were confirmed by observation of inter-residue NOEs in the NOESY spectrum. 

Other authors have attempted to rationalize the enzyme selectivity toward sugar derivatives by simulating the interaction of the substrates with the enzyme by molecular modeling [100], although this is not an easy task [101]. The first published example related to the regioselective acylation of sucrose [102]. However, the two observed acylation sites of sucrose were not on the same monosaccharide unit, and therefore a possible explanation of subtilisin selectivity could reside in the different steric hindrances. 

In higher animals as well as in My cobacterium,207 yeast,208 and Euglena, the fatty acid synthase consists of only one or two multifunctional proteins. The synthase from animal tissues has seven catalytic activities in a single 263-kDa 2500-residue protein 209 The protein consists of a series of domains that contain the various catalytic activities needed for the entire synthetic sequence. One domain contains an ACP-like site with a bound 4 -phosphopantetheine as well as a cysteine side chain in the second acylation site. This synthase produces free fatty acids, principally the C16 palmitate. The final step is cleavage of the acyl-CoA by a thioesterase, one of the seven enzymatic activities of the synthase. See Chapter 21 for further discussion. 

Figure 13.2 A possible specificity mechanism for the prevention of the misacylation of tRNAVal with threonine, (a) The hydrophobic acylation site discriminates against threonine, (b) The hydrolytic site specifically uses the binding energy of the hydroxyl of threonine for a binding or catalytic effect. The translocation may occur as illustrated via a 2 - — 3 -hydroxyl acyl transfer. [From A. R. Fersht and M. Kaethner, Biochemistry 15, 3342(1976).]...

Johnson, J. L., Cusack, B., Hughes, T. F., McCullough, E. H., Fauq,A., Romanovskis, P., Spatola, A. F. and Rosenberry, T. L. (2003). Inhibitors tethered near the acetylcholinesterase active site serve as molecular rulers of the peripheral and acylation sites. J. Biol. Chem. 278,38948-38955. 

Several amino acyl constituents crucial for the protein s function are particularly vulnerable to radical damage (Roshchupkin et al., 1979 Singh et al., 1982 Sies, 1986), as shown in Scheme 2.2 and Table 2.2, with the consequences of oxidative modification. It is generally accepted that reactive oxygen species can react directly at several of these sites on a protein in addition, in some instances, when protein radicals are formed at a specific amino acyl site, they can be rapidly transferred to other sites within the protein infrastructure, the pathway so far proven being illustrated in Fig. 2.14 (Butler et al., 1988). 

Most aminoacyl-tRNA synthetases contain editing sites in addition to acylation sites. These complementary pairs of sites fimction as a double sieve to ensure very high fidelity. In general, the acylation site rejects amino acids that are larger than the correct one because there is insufficient room for them, whereas the hydrolytic site cleaves activated species that are smaller than the correct one. 

Similarly, acyl-CoA conjugates can react with proteins (protein acylation). Fatty acids covalently bind to cysteine acylation sites. This process, which modifies the properties and the function of the protein, is believed to play a key role in the regulation of the cellular machinery. Drug acyl-CoA conjugates also interact covalently with plasma proteins, namely albumin. 

The random mechanism followed by COT indicates that the substrate sites are well-formed in the resting enzyme. In contrast, in the resting state of CPT-II, the carnitine site is either closed or unformed so that binding of carnitine alone is poor. The confor-mationally constrained inhibitors do bind to CPT-II because mixed inhibition is observed when either the acyl-CoA or the carnitine substrate is varied. (If the inhibitor could bind only to the acyl-CoA-enzyme complex as is the case for carnitine, competitive inhibition would be observed when carnitine was varied). Thus, the structure of the tetrahedral intermediate found in these inhibitors induces the change in the carnitine site that is normally induced by CoA. Clearly, the affinity at the acyl site contributes strongly to the... 

D Souza C, Nakano MM, Corbell N, Zuber P. Amino-acylation site mutations in amino acid-activating domains of surfactin synthetase Effects on sutfactin production and competence development in Bacillus subtilis. J Bacterial 1993 175 3502-3510. 

Liu, J., Hughes, T.E., and Sessa, W.C. (1997). The first 35 amino acids and fatty acylation sites determine the molecular targeting of endothelial nitric oxide synthase into the Golgi region of cells a green fluorescent protein study. J. Cell Biol. 757(7), 1525-1535. 

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