4d9k
From Proteopedia
Crystal structure of Escherichia coli Diaminopropionate ammonia lyase in apo form
Structural highlights
Function[DPAL_ECOLI] Catalyzes the alpha,beta-elimination reaction of both L- and D-alpha,beta-diaminopropionate (DAP) to form pyruvate and ammonia. In vitro the D-isomer of serine is degraded to pyruvate, though very poorly; other amino acids (L-serine, D- and L-threonine, D- and L-beta-Cl-alanine) are not substrates. In vivo allows poor growth on L-DAP or a DL-DAP mixture but not on D-DAP alone, this may be due to a poor promoter. DL-DAP is toxic in the absence of this enzyme, it may inhibit enzymes involved in the synthesis of pyruvate and aspartate, as well as amino acids derived from them.[1] [2] [3] [4] Publication Abstract from PubMedPyridoxal 5'-phosphate (PLP)-dependent enzymes utilize the unique chemistry of a pyridine ring to carry out diverse reactions involving amino acids. Diaminopropionate (DAP) ammonia-lyase (DAPAL) is a prokaryotic PLP-dependent enzyme that catalyzes the degradation of d- and l-forms of DAP to pyruvate and ammonia. Here, we report the first crystal structure of DAPAL from Escherichia coli (EcDAPAL) in tetragonal and monoclinic forms at 2.0 and 2.2 A resolutions, respectively. Structures of EcDAPAL soaked with substrates were also determined. EcDAPAL has a typical fold type II PLP-dependent enzyme topology consisting of a large and a small domain with the active site at the interface of the two domains. The enzyme is a homodimer with a unique biological interface not observed earlier. Structure of the enzyme in the tetragonal form had PLP bound at the active site, whereas the monoclinic structure was in the apo-form. Analysis of the apo and holo structures revealed that the region around the active site undergoes transition from a disordered to ordered state and assumes a conformation suitable for catalysis only upon PLP binding. A novel disulfide was found to occur near a channel that is likely to regulate entry of ligands to the active site. EcDAPAL soaked with dl-DAP revealed density at the active site appropriate for the reaction intermediate aminoacrylate, which is consistent with the observation that EcDAPAL has low activity under crystallization conditions. Based on the analysis of the structure and results of site-directed mutagenesis, a two-base mechanism of catalysis involving Asp(120) and Lys(77) is suggested. Crystal Structure of Escherichia coli Diaminopropionate Ammonia-lyase Reveals Mechanism of Enzyme Activation and Catalysis.,Bisht S, Rajaram V, Bharath SR, Kalyani JN, Khan F, Rao AN, Savithri HS, Murthy MR J Biol Chem. 2012 Jun 8;287(24):20369-81. Epub 2012 Apr 13. PMID:22505717[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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