ACY1

Acylase I (AA1, aminoacylase I) is a member of the aminoacylase family of enzymes that deacetylate a broad range of substrates. It is a homodimeric zinc-binding metalloenzyme located in the cytosol, which catalyzes the hydrolysis of N-acyl groups in L-amino acids, including the N-acetylated derivatives of serine, alanine, glycine, methionine, glutamic acid, leucine, and valine.

Classification

Acylase I belongs to aminoacylases. Aminoacylases have been classified into four groups: acylase I (EC 3.5.1.14, N-acylamino acid hydrolase), aspartoacylase (EC 3.5.1.15, N-acetyl-L-aspartate amidohydrolase), acyllysine acylase (EC 3.5.17, N-acetyl-L-lysine amidohydrolase), and acylase III. Acylase I shows a preference for aliphatic N-acyl-R-amino acids. Aspartoacylase and acyllysine acylase are selective for N-acetyl-L-aspartic acid and N- acetyl-L-lysine, respectively. Acylase III shows a preference for N-acyl aromatic amino acids. Acylase I is well-characterized by a zinc-containing, homodimeric protein with a subunit Mr of 43,000. Acylase III has not been studied in detail. Acylases I and III may catalyze the observed hydrolysis of xenobiotic-derived mercapturates (S-substituted-Nacetyl- L-cysteines) in vivo in rabbits, rats, and guinea pigs and by rabbit, rat, and guinea pig kidney and liver tissue extracts.

Biological Function

Although a large number of studies have been devoted to the intracellular catabolism of various proteins, little is known so far about the degradation of the N‐acylated proteins, which can amount to as much as 50% to 80% of the total soluble proteins in various cell lines. Scientists have suggested that the final step involved in the catabolism of N‐acylated proteins might be due to the combined action of two complementary enzymes, N‐acylpeptide hydrolase, which generates the N‐acylamino acid from the corresponding N‐acylpeptides, and acylase, which releases the free N‐terminal amino acid. It was recently suggested that acylases might play a role in the bioactivation of some xenobiotics, as well as participating in the interorgan processing of xenobiotically derived amino‐acid conjugates. Moreover, porcine intestinal and kidney acylases I have been successfully used to catalyze the synthesis of N‐acyl‐l‐methionine derivatives in aqueous media, which suggests that acylase I might also be involved in protein acylation in vivo and that it might take part in the acylation process together with acetyltransferases.

Acylase I-Catalyzed Deacetylation of NAC

The deacylation of N-acyl-L-amino (NAC) acids is catalyzed by aminoacylases. NAC is an antioxidant with chemopreventive and therapeutic effects and is used clinically for the management of acetaminophen toxicity and congestive and obstructive lung disorders. NAC may act directly as an antioxidant or may serve as an L-cysteine prodrug and, thereby, support glutathione synthesis. Although NAC has been proposed for the therapy of HIV-1 infections, treatment of patients with AIDS with NAC failed to increase glutathione concentrations in plasma or peripheral blood mononuclear cells. NAC is deacetylated in isolated hepatocytes and supports glutathione synthesis in these cells. Also, human endothelial cells, rat lung, intestinal, and liver homogenates, and human liver homogenates catalyze the deacetylation of NAC.

Acylase I Deficiency

In EBV transformed lymphoblasts, aminoacylase I activity was deficient. Loss of activity was due to decreased amounts of aminoacylase I protein. The amount of mRNA for the aminoacylase I was decreased. DNA sequencing of the encoding ACY1 gene showed a homozygous c.1057 C > T transition, predicting a p.Arg353Cys substitution.

High amounts of N-acetylated amino acids were detected in patients with aminoacylase I deficiency, including the derivatives of serine, glutamic acid, alanine, methionine, glycine, and smaller amounts of threonine, leucine, valine, and isoleucine. Among the proteolytic systems known to be involved in intracellular catabolism of intrinsic proteins, the intracellular catabolism of N-acetylated proteins is mediated by the ATP-ubiquitin-dependent proteasome. This large complex degrades proteins into peptides 5–30 amino residues long. N-acetylated peptides are then cleaved by acylpeptide hydrolase with the release of the N-acetylated amino acid and a shorter free peptide. In the next step, aminoacylase I hydrolyzes the N-acetylated amino acid to acetate and its free amino acid.

Applications

Aminoacylases are found in a wide variety of plants, animals and microorganisms, and many of these enzymes are classified in the M20 family of metallopeptidases. Acylase I is an important enzyme in amino acid metabolism in organisms, and is one of the leading 10 enzymes used in biotechnology, due to its industrial applications and chiral specificity. The most commonly used sources of Acylase I are porcine kidney and fungi such as Aspergillus oryzae and Aspergillus melleus. Acylase I, a readily available and inexpensive enzyme mainly used in the industrial production of enantiopure L-amino acids from their N-acetyl derivatives, is shown to hydrolyze the esters and amides of natural and non-natural amino acids with high enantioselectivity. Acylase I catalyzes the asymmetric hydrolysis of N-acetyl-DL-amino acids to L-amino acids and unhydrolyzed N-acetyl-D-amino acids. Acylase I has also been successfully applied to the enantioselective acylation of alcohols and amines in organic medium.

References